REPORT OF THE DIRECTOR AND STATE GEOLOGIST I'D 1 



Frequently the offshoot which gives rise to a tourmalin mass 

 or band consists of nearly pure quartz instead of granite, and 

 every gradation between the two may be traced. Evidently, in 

 tli is instance, the quartz is playing (ho role of an intrusive, being 

 the ultra-acid phase of igneous activity. 



As stated above, the southern end of Wells island is made 

 up of gneiss, but on account of the intermingling of the Iwo for- 

 mations by intrusion, and the gneissic character of much of the 

 schist, fhe lines between them can not be accurately drawn. 

 Along the approximate lines of contact, east of Thousand Island 

 Park, there are some fine instances of dikes and inclusions. 



Near the southwest corner of the island, in 'the neighborhood of 

 Grandview Park, a very coarse and massive granite-gneiss ap- 

 pears. The relation of this rock to the ordinary granite-gneiss 

 could not be determined, no data being found to decide the mat- 

 ter. As the rock is the same as the well-known granite of Grind 

 stone island, this point is best considered in connection with the 

 latter. 



Grindstone island, though two thirds as large as Wells, is much 

 less varied in its geology. It consists for the most part of the 

 coarse hornblende granite, with scattered masses of quartzite and 

 schist, forming ridges of some extent, and also appearing in num- 

 berless inclusions in the granite. As these quartzites and schists 

 are identical in character with those described above, they de- 

 mand no farther consideration. 



The granite ranges from very coarse to very fine in grain, and, 

 though usually rather massive, always shows a trace of foliation, 

 and often passes into a well foliated gneiss. The color is gener 

 ally red, but may become grayish. It is a hornblende biol ile 

 granite, usually with much quartz, which is either bluish or 

 opaque white. 



As above indicated, this granite bears to the schists and quartz- 

 ite the same relation as does the gneiss of Wells island, and all 

 (he phenomena of dikes and inclusions are repeated in it, with the 

 exception of the tourmalin contact zones, none of which were 

 seen. 



