Review of the Neio York Geological Reports. 153 



then become by degrees siliceous, and finally, a siliceous deposite, 

 nearly pure, takes their place. Here we have an interesting ex- 

 ample of a series of changes in the transported sediment during 

 the period of deposition of this division ; yet, at the same time, 

 so imperceptible is the blending of adjacent strata, that it carries 

 with it the conviction that no link in the chain is wanting ; that 

 nature has been permitted in that region, quietly and without in- 

 terruption, during a long period of time, to do her work. 



The Potsdam sandstone, the base of this group, is the oldest 

 fossiliferous rock yet known in the United States. 



It is in the middle portion of the Champlain division that the 

 family of trilobites first appears, and there, also, are they most 

 abundant. The genera Isotelus, Cryptolithus, Calymene, IUcb- 

 nus, Bumastus, Ceraurus, are mostly confined to it. The so 

 called Fucoides demissus, now supposed to be a coralline, belongs 

 exclusively to the early part of this division. That curious fos- 

 sil, the Graptolite, is peculiar to these rocks. The greater num- 

 ber of species belonging to the genera Leptcena, Orthis, Atrypa, 

 Delthyris, Cypricardites, are found in the Champlain division. 



The western equivalents of the Champlain division, seem to 

 be the magnesian limestones and sandstones between the mouth 

 of the Wisconsin river and. the falls of St. Anthony ; and the 

 lowest limestones of the Ohio valley, i. e. the blue limestones and 

 marls of the reports on Ohio and Indiana. 



From a comparison of the fossils of this division with those of 

 Great Britain, Dr. Emmons is of opinion that its English repre- 

 sentatives are the Bala limestone and the lower Silurian. 



The Ontario division is composed of reddish sandstone and 

 fossiliferous shales below ; limestones and calcareous shales in the 

 middle portion ; red shales, gypseous shales, platerstone and wa- 

 ter limestone in its upper part. The fossils of this group are, on 

 the whole, not so abundant and remarkable as those of the prece- 

 ding group. Two peculiar species of Fucoides belong to it ; also, 

 disk-shaped and pentangular entrochites, tentaculites ; the genera 

 Littorina, Cytherina, Avicula, a species of Atrypa, and Orthis, 

 a Lingula, a Strophomena, Asaphus, and portions of two pecu- 

 liar species of trilobites, to which the generic names of Hemi- 

 crypturus and Eurypterus have been given. Also, a new genus 

 of Crinoidea, called Cariocrinvs. 



Vol. xlvi, No. 1.— Oct.-Dec. 1843. 20 



