59 o THE POPULAR SCIENCE MONTHLY. 



already at hand, collected by European observers, that tie glacial 

 epoch itself was not continuous, but intermitted by a warmer time 

 during which the ice retreated to reoccupy that portion of its former 

 territory from which it has now finally retired. Prof. Dana has con- 

 tributed some evidence of a similar action on North American terri- 

 tory. But for our present purpose a general view of the Ice period is 

 all that we need. Evidence is at hand that the glacier, at the time 

 it traversed our territory, was accompanied by plants and animals 

 different from those now inhabiting the Atlantic States. 



Remains of the reindeer have been discovered by Prof. Dana in 

 clay-beds thrown together by the action of ice. This animal is now, 

 as we know, confined to arctic regions, but then ranged the valley of 

 the Connecticut. And there has been a sort of natural trap set for 

 the animals and plants of that time, which caged a part of them, so 

 that we may examine some of their live descendants. 



It has been found that the condition of the tops of high moun- 

 tains, such as Mount Washington in New Hampshire, and that of 

 high northern regions, are very similar. It is calculated that a change 

 of one degree Fahrenheit takes place in the temperature for every 

 three hundred feet of vertical height. On a level the same change 

 occurs for every sixty miles as we journey northward. We should have 

 to travel, for instance, from Boston to Hudson's Bay, as Agassiz has 

 shown, before passing over the same range of climatic changes as we 

 do in one day in the Alps, thus causing a narrow strip of Alpine flora 

 to correspond to a broad zone of northern vegetation. The moun- 

 tains are thus compressed models of the physical conditions of the 

 latitudes of the surface. 



In the tropics we have mountains crowned with ice, whose summits 

 reproduce the condition of the north-pole ; and, as we descend their 

 sides, we pass through belts of climate ever increasing in warmth, to 

 the plain beneath, where we meet with the condition of the torrid 

 zone. Now, during the glacial epoch, when the surface of our Middle 

 States was covered with a coat of ice, the plants and animals had 

 been swept southward of the White Mountains. They bloomed and 

 lived in the spring-tides that softened the edge of the glacier, and 

 enjoyed the short summer that there ensued at the source of streams 

 fed from the melting ice. But, when the glacier retired, the summers 

 over this region becoming longer, and the winters shorter, plants and 

 animals followed the ice and their congenial climate northward to the 

 valleys of New Hampshire. Out of these valleys the glacier finally 

 departed also, but not without" leaving some of its retinue behind. 

 Alter the main glacier had left the valley, Mount Washington and 

 Mount Adams still remained largely covered with ice, and a system 

 of local glaciers filled the clefts and gorges of the hills. Allured by 

 these, some of the plants and insects were retained and did not follow 

 the bulk of their companions who were on their long march to the 



