On the Erratic Formation of North America. 83 



stratified clays and sands of the upper portion. The drift is a mix- 

 ture of blocks, pebbles, sand, and mud, mingled without order. The 

 pebbles and blocks are always rounded and covered with striae. 

 Although the geologists, MM. Rogers, Lyell, &c., who have ex- 

 amined this formation, have insisted that it contains no fossil, MM. 

 Desor and De Pourtalis have discovered some in the neighbourhood 

 of New York. The species are numerous ; the principal are, Venus 

 mercenaricB, Ostrea canadensis ^ Nassa trivittata, My a arenaria, 

 Purpura floridana, &c. They .are all now living on the shores of 

 the bay of New York, with the exception of a Solecurte which now 

 lives on the coasts of the Carolinas. 



The clays and sands which form the second stage of the erratic 

 formation, have, for a long time, been regarded as tertiary, but M. 

 Lyell having recognised them as younger, has composed his pleisto- 

 cene formation of them. 



These two stages occupy an immense space. We may follow them 

 into the north and east of the Union, over a length of 1200 miles, with- 

 out interruption. With regard to the level of the erratic phenomenon 

 taken as a whole, it rises almost to the summit of the White Moun- 

 tains. We there find polished surfaces and blocks as high as 6500 

 feet; the extreme summit, however, 6300 feet in height, has neither 

 blocks nor polished rocks. The drift rises to two thousand and some 

 hundred feet. 



The terraces on the shores of Lake Erie at 680 feet of elevation, 

 appear to be the upper level of the pleistocene. It is said, however, 

 to reach 900 feet in Canada. 



M. Desor insists particularly on this, that the clays contain fossils 

 very well preserved, that the same species are found in localities very 

 remote from each other, and that they still live on the shores of Ame- 

 rica. The level of these fossils above the sea, which it is important 

 to determine, is not everywhere the same. Along the coasts of 

 Maine, it is from 70 feet to 80 feet; it rises in proportion as we 

 advance into the interior of the country ; on the borders of Lake 

 Champlain it is about 220 feet, and at Montreal 500 feet. We 

 must conclude with M. Desor, that one of two things has happened, 

 either that the elevation which has caused the sea to retreat within 

 its present limits, has been felt with variable intensity at different 

 points of the Continent, or rather that the shells have lived at dif- 

 ferent periods at these different points, so that each of these regions 

 has formed successively the shore where these shells were developed. 

 However this may be, it follows, as an examination of the land of 

 Scandinavia had already demonstrated, that the erratic phenomenon 

 comprehends a long period full of important events. 



No one in America disputes the changes of level which that Con 

 tinent has undergone during and after the erratic phenomenon. But 

 the whole of these phenomena are explained in three different ways; 

 \st^ The theory of waves of translation, advocated by M. Rogers, 



