April 3, 1876.] ■^"♦^ [Price. 



surface covered with water-rounded stones of every size and kind, which 

 had to be gathered into stone fences before the soil could be reached 

 for cultivation ; yet so rounded are they that they readily roll out of place, 

 though the base of the enclosure be broad. These are the natural product 

 of a water-covered surface ; of waters floating ice ; which ice may have 

 been thick as Greenland hummocks' ice-belt ice, or glacial icebergs, borne 

 on the arctic current that now comes southward along the eastern side of 

 our continent. We see the evidences that as the ocean retired, the eleva- 

 tion made successively of every part of New England a sea-lashed shore, 

 leaving the drifts that the waters had spread over the sea bottom. 



The glacialists seizing upon the one seemingly sufficing adequate cause of 

 a great ice sheet, overlook the difficulties which that theory must encounter 

 to account for that cause, and also other means that may more naturally 

 account for the seen results, without resorting to any abnormal freak or ec- 

 centricity of Nature. They may notice that the grooves very generally 

 conform to the trend of the high valleys and watersheds and to the course 

 of the currents when wide areas were beneath the sea ; denoting the de- 

 scent of mountain glaciers, or the transportation by water of ice rafts, or 

 icebergs. They refer not to the transporting power of water in times of 

 ice-floods, when mountain sides slid down, and lakes broke through their 

 moraine dams. They take the presence of irregular boulders in the under 

 clay of the drift as the sure evidence of the work of the polar ice-sheet, 

 while the presence of the like boulders in all the drift, as we see here in 

 Philadelphia, is not taken as proof that all the other strata of the drift had the 

 like cause. The heavy boulders they see at a higher level than their parent 

 place in situ, they suppose could only reach their elevations by being 

 pushed up by the great continental ice-sheet because it must obey the 

 pressure of the great ice-head at the pole, and approximating the level of 

 that source of pressure, rises over the secondary mountains of New Hamp- 

 shire, the Katahdin of Maine, and bridging sounds and inlets of the seas 

 passes into the Atlantic. It is overlooked that those boulders may rest on 

 elevations that may have risen out of the sea from a lower level than the 

 parent quarry ; or may have been shoved higher by the back currents of 

 water that will drive ice-sheets high upon each other when they encounter 

 obstruction ; while on the other hand the ledges of rock that yielded the sup- 

 ply may have sunk lower, by the earth's oscillations, or have been ground 

 down by floating ice, after higher rocks had been carried awaj^. 



It is said the glacial epoch was so recent that the mountains were 

 already so degraded as to be near their present height when that epoch 

 come on, and could not liave been cause of the effects seen. Now the last 

 glacial epoch is placed many thousand years ago ; Geikie says more than 

 two hundred thousand years. We will not hold him to exact figures; but take 

 it that was near the time, then it appears to have been ample for the 

 mountains to become reduced from a much higher elevation than their 

 present size, by the operation of normal causes, but anciently acting with 

 greater activity. Now in every year since they rose the height of the 



PROC. AMER. PHILOS. 80C, XVI. 97. 2h 



