356 Review of the New York Geological Reports. 



making us acquainted with the earhest forms of organic existence 

 to which geological science can point back. 



Here is a representation of one of the Plate 68, p. 268, Emmons's 

 lowest and oldest fossils now known in Heport. 



this country. And what is worthy of 

 note, though a species peculiar to the 

 Potsdam sandstone, it belongs to a genus 

 which has survived all the changes upon 

 the earth, and, as Mr. Conrad justly re- 

 marks, has lived through all ages of or- 

 ganic existence ; even at this day, it is 

 an inhabitant of the ocean. Linguia antiqua. 



At Birmingham in Essex Co., N. Y., at a place called the High 

 Bridge, this Linguia is abundant, though obscure, in the Pots- 

 dam sandstone ranging through the strata to the depth of seven- 

 ty feet. There is another fossil in this rock between Wilna and 

 the Natural Bridge, in Jefferson Co., N. Y., which Prof E. says 

 resembles the so-called Fucoides demissus, but no figure is given 

 of it. 



The lower part of this rock is usually a conglomerate contain- 

 ing sometimes, as Dr. E. informs us, masses of quartz as large 

 as a peck measure. The upper part is usually a white friable 

 sandstone, a yellowish brown compact sandstone or a hard quartz 

 rock. The entire thickness of the mass on the Canada slope is 

 three hundred feet, and the belt of country which it occupies av- 

 erages about fifteen miles. 



At De Kalb in St. Lawrence Co., the Potsdam sandstone is el- 

 evated by disturbing forces acting from beneath, and '' seems also 

 to have been subjected to lateral pressure, by which the strata are 

 folded around each other ;" but in general this rock is even bed- 

 ded. It rests directly either on gneiss or granite, and borders the 

 hard crystalline rocks on the N. and N. W. along the line of road 

 leading from Ogdensburg on the St. Lawrence, to Plattsburg on 

 Lake Champlain. The most interesting locality for the geolo- 

 gist to examine it, is on the Au Sable River, near Birmingham 

 and Keesville, where he can observe its characters in fossils, and 

 contemplate its stratification in frightful gorges. 



Its western equivalent is not yet fully determined. Along the 

 Wisconsin River, towards its mouth, a sandstone is visible close- 

 ly resembling the Potsdam sandstone of New York in external 



