2l6 ROCHESTER ACADEMY OF SCIENCE. [Oct. 23, 



tropic seas, requiring pure water and violent wave action ; or the 

 detritus may be far borne by currents and left as a fine, structureless, 

 organic sediment. If derived from the destruction of older lime- 

 stone rocks, the lime sediment may be mingled with other silt in any 

 proportion. 



Aqueous sediments of volcanic origin are distinguished by their 

 niineralogic character, and deposits entirely of meteoric origin are 

 confined to ocean areas far from land. 



Beneath the city of Rochester the drill has penetrated to a depth 

 of over 3, coo feet, giving us fortunately a section (') of the under- 

 lying strata down near to the crystalline ba^e. From the character 

 of these rocks we may read the main events in the history of this 

 locality since Archean time, for even geological history with its' 

 "millions of years" has its early period of the unknown. What the 

 local conditions were during Archean and Algonkian time, a duration 

 as great, perhaps, as all time since, we can only conjecture. This 

 area may have been a portion of the early land mass, which supplied 

 by its destruction the material for Archean strata or from the 

 earliest time it may have been continually under the continental sea. 



The following table gives the Rochester strata in order of 

 superposition, the oldest at the bottom : — 



Condensed Section of the Rochester Strata. 



Magnesian limestone 6o+feet, Niagara Group. 



Dark shale ' So " '• " 



Limestone and shale partings i8 " Clinton Group. 



Green an-d purple shale. 24 " " " 



Limestone.- 14 " " " 



Green shale 24 " 



Red sandstone and shale 1075 " Medina Group. 



Blue and gray sandstone- - 83 " " (Oneida) Group. 



Dark shale. - 598 " Hudson-Utica Group. 



Dark limestone 954 " Trenton Group. 



Gray limestone.- - 4° " Calciferous Group. 



Dark shaly limestone. - 50 " " " 



Black magnesian limestone. 44 " " " 



Dark calcareous shale - 3 " " *' 



White siliceous mragnesian limestone. 2 " (?j 



Ferruginous quartz (?) (?) 



(i) The record of this well is published in detail in these Proceedines, Vol. i, pp. 182-186. 

 " A Section of the Strata at Rochester, .\. V.. as shown by a deep boring. ' By H. L. Fairchild. 

 Republished with notes in article by C. S. Prosser in this Volume, pp. 91-92. 



