72 NEW YORK STATE MUSEUM 



have never been highly folded or severely compressed. Many 

 broad belts of the strata are known to be practically horizontal or 

 only very moderately folded, while many masses are merely tilted 

 or domed at various angles. Very locally the strata exhibit con- 

 tortions. The many scattering bodies of Grenville strata through- 

 out the Adirondacks do not show any very persistent strike as 

 would be the case had they been subjected to notable erogenic 

 pressure. 



The structural relations of the Adirondack Grenville strata are 

 reasonably explained as having been the result of the slow, irregular 

 upwelling of the great bodies of more or less plastic magmas, 

 probably under very moderate compression, whereby the strata, 

 previously deformed little or none at all, were either broken up, 

 tilted, lifted or domed, or engulfed in the magmas. According to 

 this view, many large blocks or belts of Grenville strata, or several 

 such rather locally separated by intrusive masses, with strike of 

 intrusive masses parallel to the strike of the Grenville, show mono- 

 clinical dips ; many masses of Grenville were shifted around in the 

 irregularly rising magmas to show various strikes and dips accord- 

 ing to the direction of magmatic currents; some bodies of Grenville 

 were merely domed over bodies of laccolithically rising magma and 

 hence exhibit more or less quaquaversal strikes and dips ; some 

 masses of strata were considerably bent or even folded into syn- 

 clines by being caught between bodies of magma upwelling at about 

 the same rate; some masses, especially the more plastic limestones, 

 were locally contorted near the igneous contacts ; and many masses 

 of strata were caught up or enveloped by the rising magmas. 



The Grenville series within the Schroon Lake quadrangle is not 

 extensively developed, and the exposures are mostly too scattering 

 to throw much light upon its structure, but most of the types of 

 occurrence above mentioned seem to be present, except probably 

 the laccolithic. Strikes and dips are platted on the accompanying 

 geologic map, though where several similar observations were made 

 within one-fourth of a mile of each other but one is usually 

 recorded. 



In the Minerva area the Grenville strata seem to show a synclinal 

 structure with a west-northwest strike of the axis through the vil- 

 lage, but the outcrops are too scant to make this certain. If syn- 

 clinal, it is not a very sharp fold because the dips generally vary 

 from 30 to 50 degrees. A structure of this sort may be readily 

 explained as due to greater upwelling of the granite magma on 

 both the north and south sides of the mass of Grenville causing 



