9 PALiEONTOLOGY OF NEW-YORK. 



known to us the existence and wide extent of a sandstone, which he at 

 that time regarded as far below the Potsdam sandstone of New-York. 

 This rock, moreover, charged with linguloe, trilobites, etc., showed a much 

 more prolific fauna than the Potsdam sandstone was at that time known 

 to contain. A personal exploration in 1850, and an examination of the 

 localities named by Dr. Owen, enabled the writer to place this rock in the 

 same horizon with the Potsdam sandstone, and in fact to demonstrate its 

 continuity with the more eastern deposit of this age, by tracing it along 

 the lower limits of the Silurian basin, from Canada West on Lake Huron, 

 to the Mississippi and St. Croix rivers in Wisconsin. 



The results of these examinations were published, under the writer's 

 own name, in the Report of Messrs. Foster and Whitney upon the Lake 

 Superior Land District in 1851. 



Dr. Owen subsequently adopted this view of the age of the sandstone, 

 and has thus published it in his final Report in 1852. 



The great interest of this formation in the west, is the occurrence of 

 several species of trilobites in beds which mark certain horizons in the 

 formation. The trilobites are referred by Dr. Owen to several genera which 

 he has constituted to receive them, though the forms in many instances 

 bear strong resemblances to known genera. The broken and comminuted 

 remains of these trilobites are distributed over an extent of more than 

 two hundred miles along the Mississippi river in greater or less profusion ; 

 and they are every where found, until the sandstone disappears beneath 

 the river in the northern part of Iowa. 



The lingula beds are almost equally extended, though not so prolific in 

 all parts of this range. At the falls of the St. Croix river, more than half 

 the material of the rock appears to be composed of these shells. Towards 

 the south, the beds still continue ; but the shells are broken and com- 

 minuted, and are drifted together precisely in the same manner as we find 

 seashells upon a modem beach. Here, again, over this wide area, and a 

 thousand miles from the eastern known limits of the sandstone, we find 

 the most unequivocal evidences of a shallow sea. 



