﻿GEOLOGY OF THOUSAND ISLANDS REGION 43 



dantly in the aplite dikes of the granite gneiss itself, and regard 

 the granite of the dikes as likely Picton. 



The contact relations of this rock with those adjacent are of 

 much interest. It was apparently richer in mineralizing fluids 

 than any of the other intrusives, and gives rise to interesting 

 contact rocks, to be described in the succeeding section. But 

 the field relations are also most important and interesting. 



While mapping Wellesley and Grindstone islands it quickly 

 caught our attention that the abundant inclusions with which 

 the Picton granite is everywhere charged were arranged in belts, 

 that is, along a given line the inclusions were all quartzite, along 

 an adjoining line they were all amphibolite, along another 

 nothing but granite gneiss inclusions appeared. It was also 

 seen that these belts had northeast-southwest trend, concordant 

 with the general rock strike of the region, and that further the 

 individual inclusions to large extent retained their original 

 orientation and dip, notwithstanding the intrusion. Our strikes 

 and dips, read on the rocks in the field, gave absolutely con- 

 cordant results as we passed from one inclusion to another, 

 results also concordant with the readings obtained on the same 

 rocks beyond the reach of the intrusion. We were able to map 

 the original belts of Grenville quartzite and schist, and the 

 intrusions of Laurentian granite gneiss, as accurately as though 

 the Picton granite was not present, so little had they been dis- 

 turbed by the intrusion. An attempt has been made to bring 

 out these facts upon the geologic maps. We could only account 

 for the phenomena on the assumption that we have exposed here 

 the very roof of this portion of the bathylith, the abundant 

 inclusions representing masses but just loosened from their 

 original place, not greatly sunken, and preserving unimpaired 

 their original orientation. If this be the correct interpretation, 

 the locality furnishes a fine illustration of the general phe- 

 nomenon. 



Other intrusions. While the above furnish the only examples 

 of intrusions of considerable size in the region, there are many 

 others of small size, mostly too small to map, and which it 

 seems hardly worth while to describe in detail. These are chiefly 

 of granite gneiss, and are regarded for the most part as of 

 Laurentian age, and as representing comparatively small upward 

 protrusions from the general roof of the great mass of Laurentian 

 granite gneiss which is believed to underlie the entire district, 

 except where broken through by the later intrusions. A good 



