ELISHA MlTCHKIvL SCIENTIFIC SOCIETY. 55 



that which they would assume if left under the influ- 

 ence of gravity to collect under water. Fio-ure 10 is a 

 section at rig-ht ang-les to the bedding* planes showing- 

 their mode of occurrence. 



The rock mass clearly shows evidence of considerable 

 pressure at rig-ht ang-les to the bedding- planes. This 

 is not only shown by the mass, but often by individual 

 specimens as shown in Fig-. 11, which, lying- in the posi- 

 tion it would naturalh^ assume, received the pressure 

 from above, g-iving- it its present form with the verti- 

 cal plane of fracture which has since been filled. Owing- 

 to the shape and position of the specimen, the pressure 

 would be unequally distributed, fracturing- it in the 

 direction shown for the obvious reason that the g-reatest 

 stress was in that plane. Lines of fracture are also 

 found in microscopic sections of specimens which do not 

 show it externally. Fig-. 12. 



In form, isolated specimens and those exposed on 

 the weathered surface of the rock, answer to the de- 

 scription of Emmons, g-iven above (pag-es 50, 51, and 52; 

 also see fig-ures 2-7). But when the weathered surface 

 is broken away and a fresh surface is exposed, these 

 forms are enveloped in a gfray, translucent, radial 

 fibrous mineral, which vuider the microscope proves to 

 be an impure chalcedon}^ This, as we would expect, 

 weathers g-ray- white on exposure ^ and is washed away 

 faster than the surrounding- rock. The interior, or 

 palaeotrochis proper, I find is graunlar quartz as did 

 Marsh. The small concretions prove to be chalcedon}^ 

 througdiout. There is a definite line of separation be- 

 tween the chalcedonic formation and both the surround- 

 ing- rock on the outside and the enclosed palaeotrochis. 



1. Seepag-e 54; also Text Book of Geolog-y. A. Geike — Third Edi- 

 tion. 1893. p. 69. 



