NEW YORK STATE MUSEUM 



surrounding gneiss was still fluid, since the latter penetrated 

 them to such a marked degree. Indeed, this is one of the most 

 striking features of the phenomena, minute dikes of granite, 

 sometimes strongly puckered, extending for yards through the 

 schists. 



To make Mi is possible a high degree of fluidity would seem to 

 be demanded, together with intense pressure. It is not uncom- 

 mon to find the schist a network of these minute dikes, 

 hundreds of feet from any large exposure of granil e-gneiss. 

 In such cases, of course, it is quite possible that a body of granite- 

 gmiss may lie at a small depth, or that a sheet may have been 

 eroded from above. 



As a rule, contacl metamorphiem is nearly lacking in this 

 region, but some curious examples of it are shown in Westmin- 

 ster Park, also near the highway | of a mile west, and near the 

 river bank just opposite Alexandria Bay. The schists here range 

 from nearly white to nearly black, through gray tints. The-y 

 are cut through and through by reddish granite dikes, the narrow 

 ones being massive and the broad ones quite gneissoid. Along 

 the margins these dikes frequently show much black tourmalin, 

 and this is usually most abundant in the very narrow ones, in 

 which the imperfect crystals of tourmalin interlock across the 

 entire width. At the same time, the schists along the contact 

 become impregnated with fine granular tourmalin, producing 

 strips and irregular areas of a lustrous black rock. The remark- 

 able feature about these contact zones in the schist is their ex- 

 treme irregularity in form and extent and their entire indepen- 

 dence of the magnitude of the accompanying dike. A dike of 

 granite a foot wide may have no contact zone, while a mere thread 

 of granite, a few feet distant, may be bounded on each side by a 

 band of the tourmalin rock two or three inches wide. Again, the 

 tourmalin, instead of forming a continuous band, appears in 

 lumps and bunches of every conceivable shape, irregularly scat- 

 tered along a dike, and sometimes extending several inches away, 

 at right angles to the course of the dike. 



