Geological Gleanings. 185 



as I conceive, the means of fully deciding what were the condi- 

 tions in the central and south-western part of our continent." 



" These facts, the result of so many observations, and coinci- 

 dent over so vast an area in the west, confirm conclusions drawn 

 from other sources, that the dry land and land plants first appear- 

 ed in the eastern part of the continent. Indeed we have good 

 reason to believe that dry land existed in proximity to our present 

 continent on the east from the earliest geological time, as shown 

 in the vast accumulation of materials in the Laurentian and Hu- 

 ronian periods. 



" The Potsdam sandstone, it is true, seems to be almost equally 

 spread out over the entire breadth of the country, from the slopes 

 of the Rocky Mountains, to the Atlantic; and judging from its 

 augmenting thickness in many western localities, we may expect 

 to find it, either in its normal condition or as a metamorphic rock, 

 strongly developed in some parts of the Rocky Mountains. Sub- 

 sequent to this period, however, every sedimentary formation indi- 

 cates the proximity of land on the east. The great thickness of 

 strata, coarse materials, and numerous fucoids of the Hudson 

 River group in its eastern extension, indicate proximity to land, or 

 the course of strong currents ; while in the west the formation 

 dies out in some inconspicuous fine shaly and calcareous beds, 

 which, both in the nature and condition of the material and in 

 the fossil contents, indicate great distance from land and a quiet 

 ocean. The Clinton group, in like manner, in its coarse materials 

 and abundant fucoids, points to a littoral condition of its area of 

 deposition in the east ; while it gradually diminishes in its west- 

 ern extension, and is finally altogether lost in that direction. 



"In the sedimentary rocks of the Devonian period, including 

 the Hamilton, Portage, Chemung and Catskill Mountain groups, 

 we find in Canada and Eastern New York the first appearance of 

 land plants, some of which closely resemble plants of the Coal 

 period ; and it was at that time that this peculiar vegetation be- 

 gan its existence on this continent, where we now find its remains 

 in strata of these several groups. 



" Notwithstanding this great accumulation of land-derived ma- 

 terial with its marine shells, gradually decreasing westward as 

 calcareous deposits increase — its numerous fucoids and land plants, 

 the whole series has diminished to less than two hundred feet of 

 marine sedimentary deposits in the Mississippi valley, and is there 

 marked by marine fossils only. 



