STATE GEOLOGIST. 55 



as to seem made from an earthy impalpable powder. I have 

 not had the opportunity, however, to submit any samples to the 

 inspection of a competent lithographer, which alone would 

 decide the value of the rock for this purpose. 



Rocks lower in the group are seen outcropping successively 

 along the shore of the island, from Dickinson's quarry to Pirate 

 Harbor, which, as before stated, is not more than three miles, 

 nearly along the strike of the formation, from the first appear- 

 ance of rocks of the Hudson River Group. The formation re- 

 appears on the northwestern side of the island at Brown's and 

 Seaman's quarries (790 and 796). An experimental quarry 

 of the. ship canal company was opened in this vicinity in the 

 upper part of the group- (792), but was sutsequently aban- 

 doned. The same rocks are seen at numerous points as far 

 south as the neighborhood of the old British Port, the northern 

 extremity of the point of land at the west end of the island 

 being of the Clinton Group. 



The rocks of this group contain few fossils, but among our 

 collections I recognize the Avicula, Murchisonia and Cytherina 

 (Leperdiiia?), referred to by Prof. Hall. The latter, particu- 

 laily, is characteristic at all the localities, and throughout the 

 whole vertical range of the formation. At Dickinson's quarry, 

 some arenaceous layers are seen above the Clinton rocks from 

 four to six inches thick, somewhat blotched with red, and 

 strongly ripple-marked. The resemblance to the Medina sand- 

 stone is so strong that one expects next moment to find Lingvla 

 euneata in it, but careful search has revealed no organic 

 remains. 



This group cuts across the southern part of St. Joseph's 

 Island, and passes on in the direction of the southern shore of 

 Munnusco Bay. 



6. — Niagara Group. 



The principal part of the promontory known as Marblehead 

 at the eastern extremity of Drummond's Island, is composed of 

 the Niagara limestone, so called by the New York geologists, 



