Monday, June 11, 2018

PA Mason Dixon Trail - Map 1: Gifford Pinchot State Park to Western Terminus

See this box turtle?  She represents the speed at which Kim and I completed the 200-mile long Mason Dixon Trail from Chadds Ford, PA to Whiskey Spring, PA. It only took us four years, which is about how long a box turtle takes to patrol its entire territory of a few acres - slowly. We finished our last section hike on Saturday, June 9, 2018, starting at Gifford Pinchot State Park to walk 18 miles into the Appalachian Mountains to reach the terminus with the white-blazed AT at Whiskey Springs. This turtle, which I accidentally poked with my hiking pole in high brush somewhere along the massively overgrown PA Gamelands segments of the MDT, was our spirit animal. Steady on...

Eastern Box Turtle.

The trail has veered far from the actual Mason Dixon Line northwest towards the mountains and quite a ways from the Pennsylvania-Maryland border. Today we started at Gifford Pinchot State Park at the end of the Beaver Creek Trail/Mason Dixon Trail on Squire Gratz Road. With some road walking along a busy highway, we were looking forward to getting into the woods but, whether as a prank or as a relocation, the blue blazes leading from the road to the State Gamelands trail were spray-painted black. We roamed around a bit trying to find the trail entrance from the road. It was frustrating and getting humid. We learned later that massive thunderstorms erupted to the south and east of us but we were already soaked in sweat and wet underbrush by then. We checked the MDT webpage for trail updates but nowhere did we find this confusing loss of trail. So we just started walking up the road some more and voila - found a blue blaze.

There are several SGL sections to get the hiker off-road, but we opted to skip the densely overgrown SGL 242.

It has been a very wet, rainy May and June, so I think that no matter how hard a trail crew might work to keep these wilder sections open, they quickly grow over. It was a real struggle in ankle deep mud, prickly briers, climbing over blow-downs, avoiding poison ivy, and pushing through shoulder-high grass. We'd sprayed ourselves heavily in tick repellent earlier but that did little to deter biting midges and mosquitoes. At one point we decided to do a walk-around of SGL 242 as we'd had it with bushwacking through jungle-like conditions and making such slow progress. We were worried about arriving at the car in the dark. We may have added a mile to our hike, but walking pleasantly cool and shady gravel roads through the state gamelands was just what we needed to recharge.

Squawroot, Conopholis americana.

The bulk of this section is road-walking, however, and it can be quite dangerous on narrow, curvy lanes without shoulders. Kim draped my pack with a blaze orange vest while she wore a bright orange PennState cap and orange shirt, knowing that our biggest challenge today was being seen by drivers. It kind of makes me mad that we don't have arrangements with landowners that are so common in the U.K., Scotland, and Ireland that provide for walker's right's of way across farm and pasture land. We spent the rest of our day hopping off and on roads which put a real kink in our pace.

Looking into the South Mountain hills. 

We found plenty of roadside attractions like donkey puppies. They all came scurrying from their shady run-out to say hi and get their noses petted. We saw some beautiful horses, too. A Haflinger pranced down a farm lane to greet us. A beautiful and very large black Shire with white socks galloped happily as we waved to him from the road.

Mini-Donkeys! Donkey Puppies! Wee Donks!

The day got more humid as we hiked uphill towards the mountain. Our water was running low so we spotted a small township park with a set of pavilions. Surely there would be a water spigot...

I asked a nice lady in the first pavilion if she knew where we could get water and she invited to the party! We both were so happy! Yay! Party! I had an ice-cold soda and some pretzels. Kim eyed the tray of cupcakes with anticipation. We learned a lot about the graduate as the family played a "Did You Know?" game after the gifts had been opened. My favorite was "What was Cory's favorite childhood toy?" and the answer - coming from everyone - "Anything John Deere!" These folks were wonderful trail angels. (There is a water spigot between the two pavilions - and nice bathrooms.)

Crashing a graduation party!

Refreshed, we continued the road walk ever upwards to the mountain ahead. It's been four years since we started this hike and now we were in the final two miles. Plodding onward.

Looking towards South Mountain.

Whiskey Spring Road - the last bit ( for those who start from Chadds Ford!)

Up and up we went. The midges got thicker. The mosquitoes were biting. We waved our caps around our faces and leaned into the uphill. We were now in the Appalachians and the storied Appalachian Trail would soon intersect our path and with it, the end of the Mason Dixon.

Whiskey Spring!


We reached my car and the intersection of the AT with Whiskey Spring Road. We asked a young couple to take our picture then Kim immediately went down to the spring to soak her feet. I did some stretches and peeled off a soft back brace which had soaked up about ten gallons of sweat.  I ate a handful of hiker's candy (Ibuprofen) and drank a full quart of water with some energy drink powder added. For giggles, I spread out all the section maps in the set. You can get a set by joining the Mason Dixon Trail Club. Looking down at all the places we've been brought back so many memories.

All 200 miles, ten maps.

So what's happened in four years? I earned my doctorate. Kim's kids went off to college. My grand- daughter entered middle school. Kim hiked in Arizona and Maine. I hiked in Spain, Colorado, and the U.K. I learned a ton about Mason and Dixon, the surveyors, and the landscapes through which they traveled to make "The Line." We've both connected to our local trail communities (York County, PA, and Cecil County, MD). So what happens next? Hmm. We've got our eyes on The Quad Crown!


Mason Dixon Trail System -

Saturday, June 2, 2018

NY Penn Dixie Fossil Park - Trip Log May 20

I'm way behind on posting our adventures in May. Our visit to Penn Dixie Fossil Park in Hamburg was a Christmas present to my daughter and two of her children that became a long weekend of exploring the Buffalo/Hamburg area. It was the highlight, however, and we can't wait to go back. We met local families as well as folks who had flown in from places much farther than Pennsylvania and Delaware. Our dig neighbors were from Japan, Atlanta, and just down the street. The local middle school art teacher, J.D., was a great local guide who gave us some tips for exploring the Hamburg and Lake Erie area when we return.

Fresh shale dug from the banks gave everyone the chance to claim a rock pile for the day.

We arrived at Penn Dixie Fossil Park early and joined a long line of fossil hunters. After a safety talk and introduction to the volunteer experts from the Hamburg Natural History Society and the Buffalo Science Museum, we walked through a light drizzle to an old aggregate quarry to claim a pile of rocks freshly dug for this much-anticipated annual event. Kids, grandparents, siblings, and teams of friends all claimed a spot for the day. We were lucky to have the corner of the site with three rock piles just at the edge of the banks, so the kids had plenty of space to roam and stretch their legs when they needed a break.

Aiden filled his pockets with treasures.

Kenzey listened to her favorite tunes as she reduced great slabs of stone to rubble and fossil finds.

The Devonian treasure at Penn Dixie can be kept by the finders, making this fossil park one of the most popular in the country. It claims the site of an old cement quarry and though rare, the chance of finding a golden fossil drove some kids (and adults) with intense concentration.  There's a lot of pyrite here and it can serve as one of the many minerals that replace the remains of ancient sea creatures. Just the other day a notice went up on the Penn Dixie Facebook page that a fifth grader had found a pyritized trilobite - but on our day to dig we were happy with all the trilobites, corals, clams, and brachiopods we were finding in grey, blue, and black.

Good technique, Aiden!

Em and I made sure to teach the kids proper rock hammer technique. Our love of geology and fossil hunting is a treasured family tradition and we wanted them to carry on safely with respect for the rock, themselves, and everyone around them. Gentle tap-taps with hammers and thinking about rock cleavage and fracture planes when using a small chisel kept them focused and controlled. Emily was on her game for hours, expertly popping out trilobites and other Devonian creatures.

Emily and Aiden in their Zen space - focused on each tap and pry. 
Rock saw crew helped diggers shape a larger fossil find. 

So is a fossil park really a "thing?" Well, happily for us paleo-geeks - YES! Penn Dixie was part of a national fossil park survey back in 2003 and it has since been on the forefront of defining this new kind of park for experiential learning and biogeological education. Though this rich Devonian digging site is over 380 million years old, Penn Dixie was one of the first parks to open specifically for the excitement of the dig and - best part -  being able to consult with a scientist on-site about your discovery and  keeping what you find.

Chris and his clam! At long last!

Our consulting expert was Chris, a Penn Dixie staff person and doctoral student, who was very excited about checking our keeper's bags for species of clams he was trying to document in this formation. He explained - very enthusiastically - that he had identified over a dozen bivalves here and was on the look out for one species in particular. This species, he assured us, would be a great find - one that he would add to his conference poster. It was a biogeomarker species of water temperature and oxygen level. He came by several times asking "Any clams? Got any clams?" When I showed him my two clams he used their Latin names and excitedly described their environment. "Oh! These would have been found in sub-tropical waters full of coral reefs and giant armored fish!" It was later on a stretch walk with my grandson Aiden that we found Chris down in the banks pulling up some undisturbed layers of shale. Suddenly, as we watched, he dropped his hammer and reached for a slab of stone. "MY CLAM!" he shouted. We cheered and congratulated him!

On a stretch break, Kenzey and Aiden sit atop a shale heap. "This is better than school!"

Most of Penn Dixie's visitation is composed of school groups who engage with a staff of educators and well-designed curriculum for non-formal, experiential learning. At the gathering pavilion where we received our safety talk and introductions, students assemble for sessions on Western New York's rich paleo-geological past and get to experience for themselves the excitement of fossil hunting. Besides fossil hunting, the park offers classes in ornithology and astronomy. Our dig neighbor J.D., who teaches nearby, praised the park programs and encouraged Emily to bring the kids up one summer for a week-long camp. "There's great camping nearby and so much for the rest of the family to do while they are at camp."

Emily finds a "flat" trilobite, Phacops rana.
Spoil piles are like candy for Aiden. 

I was impressed by the vast span of knowledge assembled for this big annual event. We had attended a members lecture the night before, called "Dinosaur CSI," and had met several well-known paleontologists and their families who travel in for this event. The Hamburg Natural History Society really does a great job putting this whole weekend together, but the stars of the show at the lecture were the junior rock hunters, the kids, who the scientists fawned over and encouraged for the following day's big dig. Aiden and Kenzey were pretty pumped up! (So were Emily and I!)

The thrill of looking into the past.

Our dig day took a break when the food truck arrived. People with aching backs and a few dirty dollars wandered up out of the spoils area to happily return with huge pickles, fresh-made grilled cheese, enormous Philly cheese steaks. What would the Devonian world thought of us? Would a nautilus wanted a bite of my grilled cheese? Would an armored fish steal Kenzey's cheese steak sandwich? We giggled through our lunch in the pavilion and watched many weary diggers return to their sites. Emily was eager to return. "I'm in my zone!"

Sun and drizzle teased each other throughout the day - which was perfect!

On our return,  energized by food and drink, we chatted with staff and volunteers. The fossil park, everyone said, has brought so much to the Southtowns area. Transforming the landscape from heavy industry to an economy that features natural history and conservation seems to be working in Hamburg. They were very excited for a new rails-to-trails path in development this summer. I shared how invaluable the rail-to-trails concept has been to Pennsylvania, injecting local economies with natural and historical tourism. Our visit to the Tifft Nature Preserve the day before, and exploring the  redeveloped parks of the Lake Erie waterfront the day after our dig,  all indicate that hopes are up for a greener future in the Southtowns.

A small sample of our keeper pile. Trilobites of three species in this group.
Old cement quarry-turned-best fossil park in the U.S.!

Fossil parks are the new kid on the block in the field of conservation education and while Penn Dixie is certainly one of the best, there are a few others worth mentioning here (and yes, they are on my list to visit). I had a chance to walk through the Fossil Park at Sylvania, Ohio, while on a doctoral research road trip in 2010 and at the time the quarry had not yet opened for the year. So at risk of being fined for trespass, I kept mum about my excursion into the pits at the time, but made several pages of notes about this Devonian wonderland. Just like Penn Dixie, an old quarry is given new life as a keep-what-you-find rock hound's hotspot. The Devonian seas extended farther west to Iowa and the Fossil and Prairie Park in Rockford, Iowa, makes as great an excuse to see the great savanna state as any. As with Penn Dixie, visitors come from around the world to this site. Both Sylvania and Rockford parks have excellent science-based education programs for kids and adults. More recently, new fossil parks have opened in Ohio, Oregon, North Carolina, and Washington. More information can be found in Clarey and Wandersee (2011) who conducted a survey of this new field of biogeological education parks and at the links in Notes.

Lake Erie is just ten minutes from Penn Dixie Fossil Park! 


Penn Dixie, Hamburg, New York

Clarey, R. and J. Wandersee (2011) "Geobiological opportunities to learn at U.S. fossil parks." Geological Society of American. Special paper # 474.

Fossil Park, Sylvania, Ohio

Fossil and Prairie Park at Rockford, Iowa

Wednesday, May 23, 2018

NY Tifft Nature Preserve - Trip Log May 19

Off to the edges of the Mid-Atlantic to far Western New York State for a long weekend trip with my daughter Em, her daughter Kenzey (13), son Aiden (8) for a Devonian adventure. Though this area is far removed from home, it does have a marked impact upon where we live in Central PA and Delaware. Highly charged low pressure systems fill with ocean moisture  and combine with cold fronts that pour out of the Arctic over the Great Lakes with strong winds to deliver some mighty big Nor-Easters and blizzards.  Lake Erie makes its own weather and with its abundant snow-making capability, storms roar southward to deliver our classic "lake-effect storms." Lake Erie, like all of the Great Lakes, is a fluid memory of the Ice Ages. One of our first stops was to sit on its shore and face the sunset with the remains of a once booming industrial coast at our backs. We had a paleo-lecture to attend so we couldn't stay quite till dark, but it was magic enough to imagine a mile-thick sheet of ice over our heads.

Aiden and Em snuggle for a chilly sunset on a calm but cold Lake Erie beach.

Another one of our first stops was to visit Tifft Nature Preserve just south of the First Ward district in Buffalo. This site has a heavy industrial-use history but is now blanketed in green meadows, wetlands, and forest. It was hard to remember that this was once a landfill and shipment base for coal, grain, and iron ore.  We walked through a bird-filled woods literally saturated with a wave of colorful migrating warblers where it seemed hundreds of birds were all singing at once. Yellow warblers were especially abundant and they darted here and there like bright speckles of feathered sunshine flickering through the leaves.

Cargill grain complex in the background.
Emily's capture of a Baltimore Oriole.
Emily got this great shot of a Magnolia Warbler.

Another Em capture: Bay-Breasted Warbler
Erie's industrial coast from Pennsylvania through New York is recovering its natural profile from a century of heavy industry, economic decline, and site abandonment.  Never out of view along the boardwalks and trails are the visible hulks of grain silos and steel plants.  But a transformation is taking place as Rust Belt ruin is giving way to a new green economy that capitalizes on outdoor recreation and nature appreciation. "Buffalo Rising" is a social, economic, and environmental movement that incorporates re-wilding practices as green remediation of heavily polluted wastelands while offering residents and visitors new ways to enjoy the waterfront on hike-and-bike trails, lake access for paddlers and fisherfolk, and new opportunities for the outdoor industry to thrive here.

One of hundreds of yellow warblers flitting through a very young forest.
Em tracked this Yellow Warbler into the sun for a beautiful back-lit portrait.

From the deck of the Tifft Nature Center - another Yellow Warbler!

Some of the serious environmental issues that plague Lake Erie are similar to our home waters of the Chesapeake Bay: overloading of nutrients and algae blooms, invasive species, and poor water quality. And, like at home, there are a boatload of environmental programs and organizations working hard to address these issues. There was a sense of great pride among the residents we met on our hike and certainly at the fossil dig we participated in the following day at Penn Dixie Preserve, that the lake and its shores were on the mend. Though the loss of heavy industrial jobs over the past several decades  has hurt terribly, the environmental field offers new directions and possibilities.

This corridor, an old factory road, was dripping with warblers!

Far back from the shores of the post-industrial wasteland is a hopeful economic landscape composed of precision metal manufacturing and other highly technical (and less polluting) industries. One family who intersected our hike was talking about a technical training program for their high school child.  The old industries of grain storage, coal, and steel aren't coming back despite politically charged promises that seem almost outdated and out of place in today's post industrial economy.

Aiden stands on the edge of a willow wood, partially flooded by beavers that create even more habitat.

Eco-economies are highly adaptable and need the creative energies of new generations to envision and put in place healthier more resilient infrastructures. Thinking like a beaver, with the right amount of support and structure, whole new environments can be built that reflect restoration as well as renewal.

Orioles were everywhere!

For mega-ecoregions like the Great Lakes old industrial identities die hard, while for specific communities within the Lake Erie coastal zones like Buffalo, NY, and Erie, PA, local efforts to re-imagine a wilder and greener future offer a lot of hope and excitement. We definitely felt this at Tifft Nature Preserve and Penn Dixie the next day. I'd like to spend more time here to fully explore the rewilding shores of Erie. Put that on my list.

Tifft Nature Preserve is bounded by the Southtowns of Buffalo and a redeveloping green waterfront.  Google Maps.


Tifft Nature Preserve is owned and managed by the Buffalo Museum of Science and is continuing to transform the landscape.

Tuesday, March 20, 2018

Following the Trail of a Giant: Alfred W. Crosby

The downside is that spring has been taking its time coming to South-Central, PA. It's snowing heavily again tonight. I've made the best of the sunnier days, however, to get down into the many ravines and valleys along the Susquehanna to search for signs and sounds to prove that, in fact, it is on the way.  The upside is that I've had more time to see into the woods and read the lay of land - one of my favorite things about winter.  During these weeks of exploring the deep places, the field of environmental history has lost a founder, Dr. Alfred W. Crosby (b. 1931), who greatly influenced how I look and think about land through the lens of biology and culture.

A "catwalk" trail follows a narrow ridge.

Crosby's work inspired and launched the whole new field of environmental history that includes ecology and biology as important frameworks for research and  interpretation.  His books The Columbian Exchange: Biological and Cultural Consequences of 1492 (1972) and Ecological Imperialism: The Biological Expansion of Europe, 900 - 1900 (1986) changed how I see the landscape around me. His work ignited my passion for environmental history.  By the time I graduated from high school in 1978 (and thanks to a progressive teacher in biology and evolution), I'd read and written a critical essay about Crosby's ideas of invasion biology  in The Columbian Exchange. What we see today, I summarized, is not pristine North American "nature" but the result of biological processes introduced by multiple waves of human invaders.

A wagon ford (foregound) can usually be found just before a creek's steep descent.

The myriad trails and pathways I take to access the deep ravines of the River Hills  can be made out clearly in the leafless landscape. Catwalks, the rocky, narrow ridgetop paths made by Susquehannock and earlier native peoples allow for winter views into these valleys and out across the river. Catwalks follow the spines of rocky ridges and the edges of cliffs formed by the great uplifted bedrock, sharp and boulder-filled. They aren't very safe for anyone on horseback, but their persistence as trails today show that we are still using them. Local  hunters still use catwalk trails for harvesting deer that move through the valley bottoms. I've done so myself.  Original human hunters, Indigenous people arriving after the retreat of glaciers, were the first wave of human invaders. Their mark on our landscape includes what we no longer see: wood bison, mastodon, ground sloth, giant beaver, and other megafauna that were ill adapted to human hunting pressure.

A trench ravine closes in quickly and any hope of a road is lost.

Well into a second wave of human invasion during the age of European discovery, Crosby argued that long before European settlements were established, introduced diseases had already moved rapidly ahead of them, wiping out up to 90% of native people. Diseases hit particularly hard those who lived in dense camp clusters and towns, which tended to be along rivers. Smallpox and the flu were particularly vicious, he asserts, reaching epidemic proportions long before settlers arrived. There was much evidence in our region of a plague-type epidemic: rapidly abandoned villages, empty camps, deserted horticultural sites.

A massive hemlock towers out of a deep ravine.

Crosby was very interested in how diseases traveled among both vulnerable human and non-human populations. The way was made clear for the tens of thousands of Europeans who followed the explorers because disease had preceded them. Benjamin Franklin boasted that by 1760 there were a million more "native" Britons in America courtesy of the 80,000 or so immigrants who began the process of colonization a century before. Crosby reshaped the idea of colonization in both its human and biotic history as the concept of ecological imperialism. 

Wilson Run Gorge

"These lands had to have a temperate climate, the migrants wanted to go where they could be more comfortably European in life style than at home, not less. To attract Europeans in great numbers, a country had to produce or show clear potentiality for producing commodities in demand back home in Europe - beef, wheat, wool, hides, coffee - and its resident population had to be too small to supply that demand. And so it was that so many Europeans poured into cornucopian North America, into Australasia, and into southern Brazil... bleaching out whatever Amerindian and African traces might have existed." (1) 

Otter Creek Gorge.

Crosby divided waves of Eurasian and European migrants according to how, when, and why they arrived. Eurasians crossed land bridges and introduced new hunting technologies. Europeans sailed to the New World and counted those who came for new economic opportunity or religious freedom. By 1750 up to 80% of new arrivals from Europe were indentured servants, military/naval conscripts, prisoners, and enslaved peoples from Western Africa. Economic opportunity led to exportations of products and resources back to Europe.

A trail so steep that switchbacks are marked with a triple blaze.

What was the environmental cost of ecological imperialism? The loss of native people are the saddest and cruelest chapters of Crosby's work,  but he speaks also about the exchange and demise of native animals for European oxen, horses, hogs, and poultry - even the honeybee. I've done some research on a once-common species of American bumble bee succumbing to introduced pathogens from domestically raised, packaged, and accidentally released European bumble species for a growing greenhouse industry in Canada and the Northeast. The exchange/demise is still occurring and disease is still the main factor.

What is missing?

Crosby brings attention to European naturalized weeds and grasses we can count among our biological inventories. "The eastern third of the United States and Canada, where half the population still lives, though it has been over three and a half centuries since the founding of Jamestown and Quebec, is the Neo-European seedbed of North America." (2)  On a spring day, even in the remote bottoms of these deep gorges, I can find in abundance black mustard, plantain, thistles, nettles, nightshade, dandelion, groundsel, dock, knot-grass, and mullein. Add to these, up on the cultivated plateaus of farmland and forest, all the forage crops including white clover. European flora (weeds) according to Crosby, "moved with amazing speed, sometimes bounding ahead of the settled frontier." (3)

An early-mature woodland at the edge of a ravine - this was once open pasture.

Crosby recast the human migration history of the Mid-Atlantic and Northeast as a great biological invasion and his ideas were unsettling for some established historians when Ecological Imperialism was first published. His work continues to have its critics especially among those who revere European dominion narratives and who hold history against certain ideological qualifiers. There can be no denying, however, that the spread of infectious diseases was the monumental consequence of European migration to North America. By some biological invasion histories, we are still under-estimating the numbers of native people whose deaths were attributed to smallpox. Crosby can be considered a giant among historians for his work on pathogens and contagions, but there is so much more.

Bug and Amos lead me up an old wagon road, to a steep switchback, and on to a catwalk trail.

Among his other works - some of which blew my head off when I first read them - are his books America's Forgotten Pandemic: The Influenza of 1918 (1976). This work informed my own research into the ecologies of industrial warfare, landscape of war, and WWI.  Crosby's book inspired the excellent centennial documentary Influenza 1918 shown on American Experience, PBS. Throwing Fire: Projectile Technology Through History (2002) inspired some new venues of research into the effects of biological and explosive weaponry on farmlands in my dissertation work.

Steep gradients in the river hills valleys ensured a healthy crop of mills and small factories in the 1800s.

Crosby's work inspired my fascination for the technologies of European societies that enabled exploration and exploitation across such a large global landmass. My interest in milling technologies, hydro and wind power, navigation, surveying, and time-keeping are the direct result of reading his book The Measure of Reality: Quantification of Western Society, 1250 - 1600 (1997). I remember sitting in an old gristmill-turned-nature center where I once volunteered, so totally engrossed in this book that I didn't notice the had sun set and someone had locked me in. I had to call someone with keys to come let me out. After that I got my own set of keys. Of course, this led me down a huge rabbit hole to explore the technologies, sciences, and maths of other cultures and their chain of impact on Mid-Atlantic natural history. It was a busy year of reading that had me thinking hard about going for my doctorate in agricultural history and landscape studies. Hence, my early PhD work with native bumble bees, agricultural technologies, and European imports...

Bug and Amos listen politely to a quote by Alfred Crosby.

Thinking about the influence Alfred Crosby has had on me as an environmental historian and backwoods wanderer, I looked down at my tired pups who have accompanied me on all six weeks' worth of ravine hikes. "We will content ourselves with one last archaeological trench," quoting Crosby from The Measure of Reality.  "Trench" seemed to a much safer term to use around coonhounds as compared to rabbit hole. Each ravine, every gorge, holds evidence of past cultures' impact on the land and the fact that I can see and interpret that evidence, rooted intellectual and physically in the environmental and biological consequences of colonization, we'll continue to follow the trail of the giant.  Rest in history, Dr. Crosby.

An "archeological trench." 


Crosby, A. Ecological Imperialism: The Biological Expansion of Europe, 900-1900. Cambridge University Press, 1986.

 (1) "The lands had to have temperate climates...." pg. 298.
 (2) "The eastern third of the United States..." pg. 149.
 (3)  "The weeds could move ..." pg. 162

American Experience "Influenza 1918" is available to stream and includes interviews with Alfred Crosby.

Smithsonian interview with Crosby on the Columbian Exchange.

Obituary, Alfred W. Crosby,