54 



Tribune Extrat 



I had anticipated striae, scratches, grooves, north 

 and south, aud I have since traced them across the 

 continent. There are local variations which can he 

 explained, and a tendency toward the east which 

 can he accounted for hy the easterly direction of the 

 continent and the character of tlie Atlantic coast. 

 I might say much just here on the motion of ice, aud 

 upon its reservoirs, hut I shall merely mention that 

 the movement of ice masses is meteorological, de- 

 pending on tbe moisture which falls, aud the diil'er- 

 ence in the amount of moisture in higher as com- 

 pared with lower regions. All these considerations, 

 together with ditferences of temperature, determine 

 the motion from colder to warmer, from a region of 

 greater to one of less condensation. All the condi- 

 tions which determine motion along a mountain 

 elope are not the features of the slope, but the accu- 

 mulation of moisture (snow) in the higher regions. 

 Thus the prevailing north-southerly direction may 

 be combined with local effects varying it to some 

 extent. 



All phenomena of glaciers outside of mountain 

 tracts e\hi'. it a north aud south direction, with an 

 easterly trend, which 1 think is owing to the depres- 

 sion of the Atlantic Ocean as compared with the 

 land, and were it not for this slight easterly coast- 

 elope tho line of movement in the United States 

 would be quite perfect; as it is, the deviation is 

 comparatively slight, the distinction being essen- 

 tially from north to south. This will appear very 

 evident by some additional facts. 



No part of the country yields native copper except 

 tho vicinity of Lake Superior, where it occurs in 

 large, masses. Now, bowlders of native copper are 

 found seal icred over all the Western States, hearing 

 marks of glacier.-, a. true iudex of transportation by 

 a body moving southward; for we can trace them 

 right back to their original beds. In the eastern 

 part of Massachusetts occurs the " Roxbury pud- 

 ding-stone," a peculiar conglomerate readily recog- 

 iii/ed, and you find loose bowlders of this pudding- 

 stone on this very Island (Penikese) and all the way 

 between here and Boston, but none north or west. 

 Hero are, in east and west, indications of a move- 

 ment of these loose materials, aud if you examine 

 jocks along the Great Lakes you see the Basis, as ex- 

 emplified by the presence of certain crystals for in- 

 stance. Th'Tet'ore, as a broad front extending from 

 the Rocky .Mountains to tho Atlantic, we have tho 

 marks of masses of ice all moving in the samj direc- 

 tion. 



It would bo very important to know how thick 

 the ice Was. Have we any means of ascertaing this? 

 Look at the plains about Portland (M O, or those to 

 the north of the White Mountains. They are. every- 

 where glacier-worn exhibit abundant evidence of 

 Caving beeu planed by tho advancing ice. As you 



Pamphlet Series. 



ascend the slopes of tho White Mountains you raoeS 

 continually the characteristics of glacial phenomena, 

 even above tbe clouds, for the sides of the moun- 

 tains are striated, scratched, grooved, and polished 

 in parallel lines having a north-southerly trend. 

 There is no set of hills lower than that whose sum- 

 mits are not scored. Mount Desert, 1.300 feet high, 

 is as polished, grooved, and scratched as any rock at 

 present under agency of glacial action. So that yos 

 here have the evidence that tho ice has moved over 

 them as on a level surface, and you find tho same 

 bowlders south of tho White Mountains that you do 

 north of them, showing that that range wa,s no im- 

 pediment to the glacier. Now how much higher 

 must a mass of ice be than its obstacle in order to 

 glide over it. Experiments have proved that about 

 as much ice above as below will carry the mass over. 

 Here, then, we have data for estimating that the ice 

 covering these regions aud working southward must 

 have been from 10,000 to 15,000 feet thick. Such a 

 mass is heavy, and it moves, and moves uniformly, 

 and it is to such a moving mass that wo must ascribe 

 all the present configuration of tho continent. 



By uuivorm abrasion of rocks, evenness of their 

 surfaces over a large extent, and like trend of fur- 

 rows is meant. It is quite remarkable as a pecu- 

 liarity of American drift that it consists of three dis- 

 tinct kinds. There are large expanses covered with 

 sand, loam, and round pebbles, amounting to con- 

 siderable dimensions ; and there is other drift that 

 only incloses round bowlders. You would travel a 

 long way in Europe before you found such. Why? 

 Because on this side ice covered tho whole conti- 

 nent, above which there were no mountain peaks, 

 while in the Old World, on the contrary, the gla- 

 ciers were restricted to the mountain regions, and 

 the debris which fell from tho peaks was carried to 

 the foot of some glacier, or was precipitated by the 

 way, as rough and angular as when it was torn off. 

 With us, however, the loose materials imbedded in 

 tho glacier, or plowed up by its foot, were all the 

 time grinding to powdor between tho mass of ice 

 which was Studded underneath like a gigantic rasp, 

 with rocks frozon into ib and tho solid roiik in situ, 

 over which the. glacier was moving. Thn glacial 

 phenomena of America are thus essentially dill'er- 

 ent from those of Europe. That kind of accumu- 

 lation (sand, loam and pebbles) which we find most 

 frequently, is made of the dust rocks that would 

 break up readily, and others too hard to bo reduced 

 to powder, and you thus have a mixture. But when 

 tho ice moved where tho rock was soft, there are no 

 bowlders or pebbles left in its track. This is the 

 case over Illinois and Indiana, whero no erratics 

 are found, because the rock north of those States 

 was too soft to withstand the grinding power of the 

 glacier. Clay slates, clay limestones, &c., when 



