. Biology in America. Biology. The Story of the Rocks 143 North America has been connected with Asia by a mass of land or "bridg:e" across Behrin<if Sea. It apjjcars likely that there was a similar "bridge" joining America and Eu- rope at this time (Lower Eocene), for many mammals were common to both continents. The canse of their migration is likewise nncertain, but nat- ural increase and competition for food may have been one of the compelling causes tlien as they are now in determin- ing animal movements. We need oidy recall the move- ments of the herds of bison, whic
. Biology in America. Biology. The Story of the Rocks 143 North America has been connected with Asia by a mass of land or "bridg:e" across Behrin<if Sea. It apjjcars likely that there was a similar "bridge" joining America and Eu- rope at this time (Lower Eocene), for many mammals were common to both continents. The canse of their migration is likewise nncertain, but nat- ural increase and competition for food may have been one of the compelling causes tlien as they are now in determin- ing animal movements. We need oidy recall the move- ments of the herds of bison, which formerly roamed across. v^-^.^'. .. # ,^||PPi|i^ ^5^3r^ Ciit'm^'': '^^^~'- fiw-K,V EoHipPus, THE '' Dawn Horse '' From a restoration by Chas. K. Knight. Courtesy of the Amerwan Museum of Natural History. our western prairies in search of food, the plague of locusts which overwhelmed the early settlers in Kansas, or the spread of the English sparrow from east to west to find an explana- tion for animal movements in the past. But possibly an- other, and even more potent factor was the gradually in- creasing refrigeration of the polar region, which occurred subsequent to the Eocene, and which culminated in the gla- eiation of the "great ice age" of the Pleistocene epoch. In the latter there is abundant evidence of the movement of northern mammals before the advancing ice, for we "find re- mains of walruses in New Jersey, of reindeer in southern France and of the musk ox in Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Young, R. T. (Robert Thompson), b. 1874. Boston, R. G. Badger
Size: 1651px × 1513px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcontributor, bookpublisherbostonrgbadger, booksubjectbiology
