1893.] FAIRCHILD— GEOLOGICAL HISTORY OF ROCHESTER, N. Y. 217 



Beginning with the oldest legible record, we have a white granular 

 calcareous rock, {^) which in age may be Calciferous,'or the previous 

 Cambrian, or, possibly, the still earlier Archean. The uncer- 

 tainty arises from our lack of information as to subjacent rock 

 which was only touched by the drill. Under the microscope the 

 grains of this siliceous limestone rock appear rounded or water- 

 worn, the effect of the grinding, transporting and assorting power of 

 water, and indicating detrital origin. This sand was deposited in 

 not very deep sea, nor very far from land, which was probably some- 

 where to the north or northeast. The particular conditions did not 

 exist long, for only some two feet of this limestone was laid down. 

 Then there came a deepening of the water, and withdrawal of the 

 shore-line, or else by the interposing of some barrier to the currents 

 the latter were checked or diverted. These changes in the 

 geography may be regarded as inaugurating a new geologic period, 

 the Canadian or Calciferous. The sediment became a silt (now 

 indurated into a calcareous shale) being the finer portion of some 

 land-deriv;ed detritus mingled with some calcareous matter. It 

 reached only the small depth of three feet when the oceanic conditions 

 of the locality were intensified, and the sediment became nearly pure 

 lime, the land silt being excluded. This dark limestone accumulated 

 to a depth of 44 feet. Then the changing geography again allowed 

 some silt to reach the area, and 50 feet of dark gray, clayey limestone 

 accumulated. Again the silt was excluded, and 40 feet of pure, drab- 

 colored limestone were formed. These Calciferous beds, consisting 

 of 134 feet of variable limestones resting upon a thin base of shale, 

 represent marine conditions, with the exclusion of strong currents 

 bearing coarse detritus. 



Concerning the life history of this period we have knowledge from 

 the fossils of the same geologic horizon accessible at other localities. 

 If any vertebrates lived they have not been found. But below the 

 vertebrates there was a profusion of animal life representing all the 

 great marine groups. Crustaceans were abundant, chiefly trilobites. 

 Mollusks predominated, especially brachiopods. Plants so far as 

 known, were wholly marine. 



(2) In the well-record as originally published (see foot-note above) this rock was called a 

 sandstone. An analysis of the sample (63), which contains some black shale derived from the 

 stratum next above, made by Mr. V. J. Chambers of the University of Rochester, gives the 

 following: — 



Insoluble in hydrocholic acid, 63 per cent. 

 Soluble in hydrochloric acid — 



CaC03 20.93 



MgC03 14.08 



Residue 1.99 37 per cent. 



100 per cent. 

 15, Proc. Roch. Acad. Sci., Vol. 2, July, 1S94. 



