22 NEW YORK STATE MUSEUM 



the further exploitation of an eurypterid fauna in the Schenectady 

 shales, the discovery of which was referred to last year. 



I^leld work on the North Creek quadrangle which has been in 

 charge of Prof. W. J. Miller was concluded by the survey of the 

 northern portion of the area during the season of 191 1. In general 

 the geology is much the same as that of the southern portion of 

 the quadrangle which was referred to in my last annual report, but 

 a few additional features deserve notice. 



The greatest single mass of syenite-granite extends from south 

 to north across the quadrangle as a belt from six to ten- miles wide, 

 and in it are a few Grenville masses or inclusions of considerable 

 extent. This great igneous rock belt is flanked on either side by 

 large areas of Grenville rocks through which occasional mountains 

 of syenite or granite protrude. The protrusion of these igneous 

 masses to heights of from a few hundred to even two thousand feet 

 above the surface of the Grenville, affords very strong evidence of 

 a decidedly irregular surface of the syenite-granite bathylith just 

 after it was cooled. In some cases faults along one or possibly two 

 sides of the mountain masses have accentuated the height of these 

 igneous rocks, but unless we postulate faults with elliptical or nearly 

 circular strikes, it is evident that much of the present irregularity 

 has been due to the irregularities on the surface of the bathylith at 

 the time of cooling. 



Eleven diabase dikes and more than fifty gabbro dikes or bosses 

 have been found within the borders of the quadrangle, and these 

 dikes show a decided tendency to arrangement into groups. The 

 two largest gabbro bosses, each measuring about a mile long and 

 from one-half to three-quarters of a mile wide, have been found in 

 the northern ])ortion of the region. One of these shows interesting 

 effects of contact metamorphism along a wide zone where the gabbro 

 breaks through pink granite. In another case a long narrow diabase 

 dike breaks through a small boss of gabbro and shows excellent 

 contact with chilled diabase margins. 



In general the Grenville, being a much weaker formation, occupies 

 the valleys, but in the north there are several well-defined exceptions 

 to this rule and the Grenville extends to the summits of small 

 mountains. 



The very interesting occurrence and origin of garnets, in a number 

 of mines in the northern ])ortion of this quadrangle and the one just 

 west, have been carefully studied in the field and laboratory studies 

 are now being made. 



