GEOLOGY OF THE NORTH CREEK QUADRANGLE 1 5 



unsatisfactory than if we were dealing with a great thickness of 

 unaltered fossiliferous strata. Hgwever, because of the excellence 

 and frequency of the exposures in most of the Grenville areas, 

 some unusually good results have been obtained though it should 

 not be understood that the statements or conclusions here given 

 are always regarded as thoroughly established. Much detailed 

 work on the adjoining areas will have to be carried on before 

 such statements can possibly be made. 



So far as can be made out from a study of all the Grenville 

 sections, the order of succession of the strata appears to be : 



5 Dark gray biotite-garnet gneiss. Thickness unknown. 

 4 Dark hornblende gneiss. Thickness at least 2000 feet. 

 3 Crystalline limestone. Thickness of some 10,000 or 12,000 feet, 



but frequently interbedded with more or less hornblende or 



pyroxene gneisses or quartzite. 

 2 Quartzite. Thickness of about 3000 feet and generally 



pure except for very thin layers of biotite gneiss. 

 I Gray, banded biotite-garnet gneiss. Thickness unknown. 



Some Grenville rocks which -are more locally well developed arc 

 not included in the above list because their stratigraphic positions 

 are wholly unknown. Among such rocks are the graphite schist, 

 the white gneiss, and the sillimanite gneiss. 



The best extensive section within the quadrangle is shown by 

 figure I which represents the succession of strata along a north- 

 east-southwest line through the Grenville area between Oven moun- 

 tain and Wevertown. The position of the section is indicated by 

 the line EE on the geologic map. This is by no means a perfectly 

 continuous section, but the outcrops are numerous enough so that 

 the condition of things shown in the figure can not be far wrong. 

 A total of from 18,000 to 20,000 feet of Grenville strata appears 

 to be shown in this section. The dip and strike of the strata are 

 pretty constant the whole length of the section, and though the 

 Oven mountain fault probably passes across the section it is not 

 thought materially to aflfect the position and thickness of the strata. 

 The hornblende gneiss toward the top of the section forms the 

 prominent ridge which extends northward to the Hudson river. 



Figure 2 represents an east-west section across the valley one- 

 third of a mile south of Daggett ])ond where there is an almost 

 unbroken succession of nearly pure limestone whose total thick- 

 ness is something like 3000 feet. On the west side, and dipping 

 under the limestone, are some beds of hornblende-garnet gneiss. 



