I04 ROCHESTER ACADEMY OF SCIENCE. [Jan. II, 



ness than it did in the eastern section, and furthermore for the lower 

 part of the section the published records of other wells have been used, 

 which although at a considerable distance from the line of this section 

 approximate nearer the actual thickness of these formations than do 

 the earlier estimates. It is well to bear in mind the fact that the 

 study of these well records is giving us more accurate knowledge of 

 the thickness of the New York formations, so that any general section, 

 carefully drawn up at present will be nearer the real thickness of the 

 rocks than it could have been before any of these records were pub- 

 lished. This point is brought out in a very clear manner by compar- 

 ing the record of the Rochester well (') with that of the Wolcott 

 well, ('■') forty-one miles east of Rochester. At Rochester, the thick- 

 ness from the top of the Medina to the top of the Trenton is 1756' and 

 at Wolcott 1720'. It may be added that in both of these wells the top 

 of the Medina as well as the top of the Trenton is sharply defined, so 

 that there can be very little doubt as to the limits of this series of 

 rocks. Leaving out of consideration all well records, a conservative 

 estimate of the thickness of this series of rocks at Rochester, based 

 on published data, would be from 1250' to 1500'. 



The following paper was read : 



PRELIMINARY NOTICE OF THE DISCOVERY OF STRATA 

 OF THE GUELPH FORMATION IN ROCHESTER, N. Y. 



By Albert L. Arey, C. E. 



In the southwestern part of this city on Frost Ave. and Summer 

 street is Pike's quarry, the top rock covered by only two or three feet 

 of soil is glaciated and nearly everywhere retains both the polish and 

 the striae left by the glacier. The rock contains very few fossils, 

 near the top a few of the characteristic Corals and Sponges of the 

 Niagara group — some ten feet below this crystals of Dolamite, Zinc 

 blende, Galenite and Flour spar are abundant : at this level two or 

 three fine Orthocerata and several specimens of Hall's so called 

 Platystoma hemispherica have been found. 



From a layer about twenty feet further down fine specimens of 

 selenite and gypsum have been taken which greatly resemble those 

 for which the Niagara of Lockport has so long been famous. 



These qualities determine the rock, the typical Niagara limestone. 



(i.) Fairchild, Proc. Rochester Acad. S;:., Vl'. I, pp. iS 

 (2.) Prosser, Am. Geol., Vol. VI, p. 204. 



[Paces 104-112 Pkinted Nov. ii, 1892.] 



