REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r35 



site, which in the main seems neither more acid nor more basic 

 than the normal rock, but differs in containing from lOfc to 30^ 

 of ferro-magnesian silicates, whereas the usual anorthosite rarely 

 has a 5fc content of these; but the greater basicity thus indicated 

 is counteracted by the more acid character of the feldspar and 

 the frequent presence of quartz. Also, this border rock shows 

 basic phases, that from the last cut being an example. No 

 analyses have been made of the rocks of this section, but they are 

 closely related to the quartz anorthosite gabbro described in the 

 report on the Mooers sheet in the 19th annual report, and to other 

 rocks shortly to be described, analyses of which are available. 

 There is also shown a probable large dike of a rock whose 

 affinities are with the augite syenites rather than the anorthosite. 



Exposures in the vicinity of Saranac 



Along the Saranac river between the lake and the village are 

 repeated ledges which furnish a good section from well within 

 the anorthosite area out to its boundary. This section shows a 

 transition from quite typical anorthosite, such as that at the 

 state dam, into an anorthosite gabbro similar to that just 

 described; it is however complicated by considerable masses of 

 gabbro, which are probaibly slightly later in age and referable 

 to the hyperites. 



Near the village the contact between the anorthosite and the 

 adjacent gneisses is exposed. The rock ridge which lies some- 

 what south of the road from the Algonquin to the village, and 

 runs parallel with it, forms the boundary of the anorthosite in 

 this direction and is composed of a quite granular anorthosite 

 gabbro, in which in general labradorite constitutes from 80^ to 

 90^ of the rock, and in which hornblende and biotite are often 

 present to the excluision of augite. The new reservoir, back from 

 the village toward this ridge, is excavated in rock (974) exposing 

 black, flinty, fine grained gneisses, w'hich have the structure of 

 granulite and the mineralogy of gabbro diorite, though the feld- 

 spar extinctions indicate andesin, and at least half is untwinned. 

 These gneisses are all cut up by a later red syenite and are 

 tremendously shattered bj' very frequent joints. The gneiss is 



