430 NEW YORK STATE MUSEUM 



tion. In the ravine of a branch of Eighteen Mile creek south 

 of Gasport lenses are of very frequent occurrence, as I have 

 noted in a previous report. East of the road leading south 

 from the village, along the edge of the stream a number of 

 these, stated by Dr Grabau to be not less than 20, have been 

 observed within the space of J mile, and others appear in the 

 ravine west of the road. These all lie in the upper part of the 

 Clinton limestone, and the majority are shown in the bed of 

 the stream, the original covering of the limestone having been 

 entirely removed, though some still show the covering layers 

 of the limestone for a foot or so in thickness, arching upward 

 over the lens, forming a domed surface of exposure. A similar 

 phenomenon is observable in the occurrence on the New York 

 Central railroad at Lewiston, where the arch and dome are 

 formed by the Niagara shale. At Gasport fossils are more 

 abundant in the lenses. At Middleport no other evidence of the 

 lenses is to be found than the single one located by the paleon- 

 tologist two years ago and largely removed at that time for the 

 purpose of obtaining its fossils. This lies on Jeddo creek on 

 the land of Mr Ewing and appears to rest on top of the upper 

 Clinton limestone and to be covered by the Kochester shale. 

 Though the shale has been removed from the lens itself, a bank 

 of it is not far away, and evidence of it is present about the 

 edges and on the lower side of the lens. 



There is some evidence of variation in the character of the 

 fossil contents of these rock bodies, according to geographic 

 position. Those on the Rome, Watertown & Ogdensburg rail- 

 road near Lewiston appear to be the most highly fossiliferous 

 of all, parts of them being impregnated with masses of sepa- 

 rated shields of the trilobite Illaenus, which have been 

 washed together and piled up like saucers; they are also very 

 rich in cephalopods of unusual species, (Orthoceracones and 

 Cyrtoceracones), brachiopods, etc. These species are appar- 

 ently less abundant in the lenses at Middleport and Gasport; 

 but we are not at present able, from the evidence in hand, 

 to determine in how far there is a meridional variation in 



