GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 5 1 



indicated by apparent fragments of shells seen on polished surfaces 

 and in section. I return these specimens to you for your ex- 

 amination. I notice that one side of the rock specimen exposes 

 something that suggests a head of Conocephalus or other primitive 

 trilobite." 



Figure 17 is a photomicro- 

 graph of a section of this rock 



and shows what appears to be a _^_^^^^^^^^^^_aa. 

 fragment of a tiny ,shell. The MK^WBfzMnra K ^FK^'\ 

 microscope failed to^ bring out 

 any structure in the concentric 



masses. 



In addition to the suggestive 

 marking referred to by Doctor 

 Clarke as possibly representing 

 a trilobite cephalon, the writer 

 noted another strongly suggest- ^.^ ^^ g^^^.^^ ^ ,^.^ ^^^,.^^ ^^ ^^^ li^^. 



ino" a HvolitheS ^*°'^^ ^^ ^^^ ^°°^ °^ Ruppert's quarry 



The rock layers in the floor of the quarry are about ten or twelve 

 feet below the layers yielding L. p i n n i f o r m i s and the whole 

 are conformable. 



The Trenton. This horizon, as mentioned above, was reported 

 by Professor Dwight from the eastern margin of the belt on the 

 farm of R. J. Kimlin and was recognized by the presence of 

 Solenopora com pact a. No other localities have been 

 described. 



Petrographic characters and further description. The Potsdam 

 rock in the locality first reported by Professor Dwight was described 

 as varying from a tough compact limestone through fissile, shaly 

 argillaceous types and arenaceous and oolitic limestones, into quartz- 

 itic varieties which were sometimes brecciated. All were calcareous. 

 These may be verified for the most part. The calcareous quartzite 

 is often friable from the loss of the carbonate and rusty from iron 

 discoloration. It frequently carries shell-like depressions or molds. 

 Along the western margin of this strip large quantities of sand 

 are dug and shipped away for molding purposes. In appearance, 

 it strongly suggests the rusty quartzitic phase of the Potsdam of 

 this western strip. As favorable a place as any for observing this 

 sand is on the farm of Mr Toel on the Camelot road north of 

 Casper creek. 



A section beginning at the eastern margin of the belt, just south- 

 east of R. J. Kimlin's farm, and running west along the Spackenkill 



