62 NEW YORK STATE MUSEUM 



of the formation here is comparable with the middle of subdivision 

 D of the Champlain section, that is, that division D and C of that 

 section and the lower part of D, are lacking here and that Beek- 

 mantown deposition at the west of the Adirondacks began cor- 

 respondingly later than in the Champlain valley. 



Canton quadrangle. Mr Martin, who has been occupied with 

 the Precambric rocks of this quadrangle, reports as follows : 



The Grenville formations and the later intrusives are about 

 equally abundant in the area examined. Nothing older than Gren- 

 ville was discovered, for these rocks everywhere rest upon later 

 igneous masses. Their total thickness is not demonstrably greater 

 than 2 miles. Of the Grenville sediments, the limestones, in vary- 

 ing degrees of purity, are perhaps the most abundant; sometimes 

 they are made up of pure carbonate of lime, but as a rule there is 

 a prominent admixture of silicates, actinolite, coccolite, phlogopite 

 and other minerals. Transitions through quartz-mesh varieties to 

 thin-bedded quartz-schists are often observed. 



Garnet-gneiss, with garnet-free varieties, is strongly developed in 

 the southeastern part of the quadrangle, but elsewhere it occurs 

 only in thin layers. These rocks are associated with limestones 

 and rusty gneisses, and the total thickness is not far from 3500 

 feet. The series has been injected by later intrusives of both 

 gabbroic or gabbro-dioritic and granitic composition, and the whole 

 doubly folded back upon itself into an immense isoclinal sigmoid, 

 now beveled by the surface of erosion. 



Silicious gneisses, occurring chiefly in the western part of the 

 sheet, comprise garnetiferous biotite schists, quartz-feldspar- 

 biotite paragneisses, thin quartzites and other transitional sedi- 

 mentary varieties. With these are sometimes associated thin 

 laminae and layers of calcareous quartzite, and some limestone 

 strata, only the largest of which are mapped separately. Minor 

 types, such as quartzite, quartz-mesh limestone, quartz schist and 

 pyritous gneiss, are of restricted development, and of these the 

 latter has the more general distribution. Certain amphibolites, in 

 the lack of precise indications as to their origin, are questionably 

 included in this series. 



The amphibolites of the Pierrepont region, on the other hand, 

 are believed to be, and those of the Little River-Pyrites belt are 

 known to be, derived from an early gabbro intrusion, and the two 

 masses are probably, though not certainly, continuous. South of 

 Pierrepont Center the basic intrusive has formed an injection zone 



