proceedings: geological society 311 



and chemical individuality of different fields that, outside of this field, 

 in Ohio and Pennsylvania they are sometimes common in large 

 aggregations in sandstones. Chert and opal growths are scarce and 

 difficult to recognize, and received no special attention. Micas are 

 probably the most significant of the secondary minerals. They are 

 of various species and types and their differentiation from syngenetic 

 micas is difficult, being based mainly on habit and distribution. These 

 most require further study, but so far as can at present be stated their 

 development seems to be, like that of the carbonates, related to cir- 

 culation resulting from opening up of wells. There were some indica- 

 tions that the development of secondary quartz and sulphides might 

 also be related to this feature. 



A final interesting metamorphic character is incipient granulation, 

 apparently by pressure and followed by recementing of sand grains 

 in a few of the deepest beds, especially in one sample at a depth of 

 2230 feet. 



Of the relation of oil to these factors nothing can as yet be said. 

 The most porous, which are generally the purest and coarsest sand- 

 stones, naturally form the best reservoirs, but they are often barren. 

 A dark brown stain, believed to be due to oil, is also found related to 

 the occurrence of carbonaceous matter in some of the clays, a relation- 

 ship well recognized in the oil shales of the west. 



The 317th meeting was held at the Cosmos Club, March 14, 1917. 



REGULAR PROGRAM 



Harry Fielding Reid: The distribution of land and water on the 

 earth. (No abstract.) Discussed by Eakix, Umpleby, and W. J. 

 Humphreys. 



William Bowie: Some evidences of isostasy. The first exhaustive 

 test of the theory of isostasy was made by Prof. John F. Hayford, 

 about ten years ago, while he was in charge of the geodetic work of the 

 United States Coast and Geodetic Survey. For this purpose he used 

 the connected triangulation of the United States and the astronomic 

 observations made at several hundred triangulation stations. His 

 results were surprisingly convincing that isostasy existed to a remark- 

 able degree. 



The speaker reviewed briefly the evidences of isostasy, as given by 

 the most recent investigations of the subject by the Coast and 

 Geodetic Survey. In these investigations there were used 219 gravity 

 stations in the United States, 42 in Canada, 73 in India, and 40 other 

 -tations, which were principally in Europe. The conclusion reached 

 by the speaker was that isostas^y, for areas as large as the United 

 States, is perfect and that it is practically perfect for areas of a much 

 smaller size; such, for instance, as the state of Texas, or an area even 

 smaller. 



It is impossible to tell, with our present data, whether the local 

 deviations from normal gravity, called anomalies, are due to a lack of 



