6i 



AyyAL6 SEW YORK ACADEMY OF SCIEXCES 



Tiie liastT examination given to tlieni leads to the belief that differentia- 

 tion effects can be traced. 



The closest relatives of the igneous rocks are the sediments, and be- 

 cause of the fact that the material constituting these sediments has been 

 furnished by the volcanic fragmental supply in large part, their character 

 and makeup is in many cases not strikingly different from the ashes and 

 finer tuff's. They do, however, represent an additional assorting, an ad- 

 ditional weathering and an additional opportunity for intermixture of 



Fig. 9. — Photomicrograph of a foraminifeial shale from the Bayarnon-Comerio road, 



magnification 2S diameters 



The dark areas are chiefly earthy aggregates or' very fine texture : the whitish areas 

 are calcareous spots which in many cases stiil preserve the forms of foraminifera. It is 

 the removal of such materials from the shales that is believed to account for their 

 porosity as seen in weathered outcrops. 



materials from different sources and of organic material developing at the 

 same time. These conditions give a great range of composition and 

 mineral makeup to the shales and sandstones and they merge by imper- 

 ceptible gradations from simple tufaceous or arkosic sediments to cal- 

 careous rocks or even to fairly pure limestones. The common source of 

 the calcareous element in these rocks is from an intermixture of fora- 



