reproduced as something like "tocai," which the British converted 

 to "turkey." In point of fact, the first of these birds were carried 

 to Spain, but it was found that they bred better in the Low 

 Countries — then Spanish — and Belgium became the great center 

 for raising them. The blue and the white varieties were devel- 

 oped there in very early days. They were then imported into 

 England, where their stock was greatly improved; and from 

 there they were finally shipped back to America to the colonists 

 in New England. There are statements of early date in the latter 

 region affirming that these imported turkeys would not breed 

 with the wild ones. 



ORIGIN OF THE HEARTLAND 



The position and configuration of this triangular heartland is 

 not due entirely to physiographic features of the land surface 

 nor even to its particular and unique climate. Initially, it has a 

 much deeper origin and cause. Once again, this is the recent (or 

 current) "ice age" and its long-term pulsations of temperature 

 and precipitation. Its past influence on this province is neither 

 obvious nor even apparent until it is pointed out to us by 

 geologists. Yet these influences were paramount, and it was an 

 icecap that created the whole physical structure of the area. 



Four major advances and retreats of the ice took place. 

 Beginning with the most distant past, these are named the 

 Nebraskan, the Kansan, the Illinoian, and the Wisconsin. 

 Between these the ice vanished completely from this province; 

 and these intervening or interglacial periods, as they are called, 

 have been named the Aftonian, Yarmouth, and Sangamon 

 respectively. The ice did not come down exactly the same way 

 each time, though on the whole it spread over much the same 

 area and tended to follow the same routes between the major 

 land surfaces. The Illinoian reached farthest south, almost to the 

 junction of the Mississippi and the Ohio. At one time or another 

 an icecap seems to have stretched from the eastern face of the 

 great barrier of the Rockies in the region of northern Montana, 

 all the way to New Jersey and northern Pennsylvania. 



The effects of these inland ice advances were very profound, 

 not only over that portion of land which they actually sub- 

 merged but for a great distance beyond, and all the way down 

 to the Gulf coast. The proximity of a large icecap means those 

 terrible adiabatic winds of which we spoke in connection with 

 Greenland (see Chapter 1), and in this case those blowing south 

 from this icecap were confined between the great mountains on 

 the west and the Appalachians on the east. The air could, in fact, 

 be almost viscous, it was so cold, and it literally poured off the 

 ice and down over the Mississippi valley. However, some inter- 

 esting facts have been discovered lately which set for us some 

 real conundrums. 



The ice must have advanced at a really terrific rate (or alter- 

 natively, according to one current theory, the crust of the earth 

 must have slipped up under the polar region at an astonishing 

 speed) because, rather than pushing all the major vegetational 

 belts southward before it, the ice seems to have ridden rough- 

 shod over them, bulldozing everything south to regions where 

 such southern woody plants as oleanders grew. Evidence of this 

 is the wood of several southern temperate trees which has now 

 been found in the icecap's terminal moraine. These trees must 

 have been growing at lower latitudes, for they needed mild 

 temperatures and a certain annual quota of sunlight merely to 

 exist. Moreover, unless the ice moved south — or, conversely, the 

 crust moved north — in less time than it takes oleander wood to 

 rot, those trees simply could not have been there, because either 



the extra-cold adiabatic winds would have killed them, or they 

 would have been transported too far north on the shifting crust 

 to regions where there simply was not enough sunlight annually 

 for anything but a few specialized alpine-Arctic plants, mosses, 

 and lichens to grow. 



This is a very important feature of this province's recent 

 history: it means that, even when a vast icecap covered its 

 northern half, the southern half, although chilled, could have 

 been and probably was initially wholly forested, so that ole- 

 anders grew in cracks along the ice front itself, just as flowering 

 shrubs grow at the very feet of glaciers in Alaska, Norway, and 

 Switzerland today. Nothing is more surprising than to be pushing 

 your way through a dense oak-elm-and-beach forest under a 

 flashing summer sun, plagued by mosquitoes in the shade, and 

 trampling on orchids, and suddenly to break out from the 

 undergrowth upon a towering peacock-blue wall of ancient ice. 

 Yet there are many places in the world, in both northern and 

 southern hemispheres, where you can do this at the feet of 

 mountain glaciers. Could ancient man have experienced similar 

 conditions at the edge of this ancient icecap? It seems from the 

 evidence of buried woods that he could have done so, and this 

 can only mean that man and animals could have camped and 

 hunted all across what is now the United States throughout at 

 least the preliminary phases of all four ice advances. This puts 

 an entirely different complexion upon our concept both of an 

 ice age and of the status of interglacial man and animals in 

 North America. In fact, whoever the people were who dwelt on 

 this continent before the Amerindians — and left such quantities 

 of beautifully made stone tools — they could quite well have been 

 hunting egrets on one side of the Mississippi at St. Louis while 

 ice cliffs towered skyward on the other. 



However, the icecap in the north had a profound effect upon 

 the south of this province, due both to winter snow and summer 

 rain and to the vast quantities of water that issued from the 

 icecap every summer when it melted along its front. The 

 southern part of the province was then very lush and much of it 

 swampy or flooded; and, since the presence of open water tends 

 to equalize the air temperature, that part of the land, though 

 close to the ice, was somewhat warmer than it would otherwise 

 have been during the autumn. 



MECHANICS OF AN ICE AGE 



An icecap may be as much as two miles thick. Ice is really a 

 kind of rock and a heavy kind at that. A two-mile thickness of it 

 piled up on land causes the underlying rock to sag. The result is 

 that the ice can thicken some more, for its surface is thus lowered 

 relative to sea level and if more snow falls, more ice is formed. 

 The ice sheet becomes thicker, and thus heavier, and exerts more 

 pressure upon the rock below, causing it to sag further. However, 

 there comes a time when the weight of the ice is so great that it 

 begins to render its own lower layers plastic so that they begin 

 to flow. Then the ice begins to move outward in all directions. 

 This may produce some very odd results because, while the 

 bottom ice may be locked in a valley, the upper layers may glide 

 over it and ride over mountains or even run uphill. 



The last icecap spread all over the Laurentian Shield — that 



Facing page, above: The Long-tailed Weasel is the com- 

 monest of this clan in the Heartland and the East, but is 

 rarely seen, being nocturnal and wary. Below: The Mink 

 ranges almost all over the continent except for deserts. 



82 



