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Geology. 431 



6. The number of terraces is usually larger and the height gi-eater on 

 the small than on Large streams; tliere are seldom over three ox four on 



the Connecticut; while on some of its tributaries, there are sometimes as 

 many as ten. 



6. The terraces on opposite sides of the same stream very often do not 

 correspond in elevation, 



^. The terraces, in general, slope with the stream. They are usually 

 somewhat the higliest about a gorge, as if the gorge had occasioned a 

 higher level to the river floods, and therefore more elevated depositions. 

 They show by the stratification that they are the result of water-action ; 

 though stranded ice, it is urged, may have aided in making the variety of 

 terrace called moraine-terrace. 



8. The beaches also must have been produced by w^ater, and this water 

 must have been the ocean. "Hence I feel sure," says the author, "from 

 the facts wliich I liave stated, that over the northern parts of this country, 

 this body of water must hav^e stood at least 2000 feet above the present 

 sea level ; and I might safely put it at 2500 feet; for up to that height I 

 have found drift modified by water." 



9. As a consequence of these conclusions, it is aigued that the drift . 

 period was a period of submergence for the larger part of the continent, 

 and perhaps nearly the Avhole, and since that period, the ocean has stood 

 2000 feet deep over New England. 



10. Tlie formation of the succession of beaches might have taken 

 place by a gradual elevation and drainage of the continent, without 

 pauses in the movement of elevation ; yet it is possible that some such 

 pauses may have taken place. Still, the author argues against the prob- 

 ability of such pauses, and finally against the possibility of pauses for 

 river ten*aces in general, on the ground mainly of their unequal heights 

 on opposite sides of the streams, 



11. As regards North America, "we may as yet safely say, that there 

 is no evidence of the existence of life in the seas that covered it during 

 the period of unmodified drift; and indeed we might say the same of a 

 considerable part of the period of the modified drift and alluvium." 



12. Glaciers probably existed on the mountain summits that stood 

 above the waters, as facts appear to show. 



13. The apparent elevation of the continent may have been a conse- 

 quence of an actual sinking of the bed of the ocean drawing away the 

 waters from the land.* 



14. The drift scratches and transportations of stone, gravel, etc, were 

 produced mainly by icebergs during a period of continental submergence. 



* It is stated here that Professor Dana has sustained this view. But in hb paper 

 on Terraces, he only suggests it as a point to be considered in the study of terraces 

 and not as an opinion he held. He has often urged tlmt any chawge of elevation 

 in the water-line of a coast, may be a result of either one, or of both, of the two 

 causes,— changes of level in the continental areas of the earth's crust or in its 

 oceanic areas, the latter having nearly three times the surface of the former. He 

 has treated the subject in a general way, and hns stated that the av^af/e elevation 

 of the land of the globe in the present epoch, above thiit in the Silurian may not be 

 more than is a necessary result of the deepening of the ocean s bed. But he has 

 no where attributed any particular case of appan^nt elevation to simply and solely 

 the dra^ins: awav of the waters by a sinking of the ocean's bottom. 



