PETROGRAPHIC GEOLOGY AND DESCRIPTIONS 389 



Arinllyte. Graywaekr. Slate.] 



No. 506. ARGILLYTE. (SUity.) 



One mile north of Carlton, on the Knife Palls railroad. 

 Ref. Annual Report, x, page 29. 



MKJ. Large sample of slate, showing the slaty cleavage crossing the sedi- 

 mentary structure. 



No section. N. H. w. 



No. 507. GRAYWACKE. 



Knife falls, just across the north channel, at the head of the second rapids, on Homestead island. 

 Ref. Annual Report, x, page 30. 



Meg. Rather fine grained, with numerous seams and patches of vein quartz. 



Mic. The comparative fineness of the grain, combined with the thickness of 

 the section, renders it impossible to individualize the finer elements, though there 

 is no reason to suppose this rock differs from others of the region. There are 

 sparsely disseminated angular grains of quartz and of triclinic feldspar which are 

 embraced in the much finer, gray, sub-opaque matrix. 



One section. 



Age. Keewatin(?) N. H. w. 



No. 508. GRAYWACKE. 



"At the extreme upper end of Homestead island, at the very point, higher up than any rock along there 

 before mentioned." St. Louie river above Knife falls. 

 Ref. Annual Report, x, page 30. 



Mt'ij. A rather light, greenish-gray graywacke of medium grain, very similar to 

 others from this vicinity. 



Mic. The section is quite thick, but shows that the rock is composed of grains 

 of quartz and feldspar in the usual greenish groundmass. 



One section. 



Age. Keewatin(?) u. s. G. 



No. 509. GRAYWACKE. 



"Some rods east of the head of Homestead island, on the north side [of the St. Louis river], about one 

 hundred rods west of the head of the rapids that there run across to the other islands." 

 Ref. Annual Report, x, page 30. 



Meg. Closely similar to No. 508. 



Mic. A graywacke of the usual type, but the greenish groundmass is not as 

 abundant as is common. Besides the usual minerals, calcite and small grains of 

 <]>/' tlote are seen, and there are a few small highly refractive, strongly double refrac- 

 tive grains which are probably xpitene. 



One section. 



Age. Keewatin(?) u. s. G. 



No. 510. SLATE. ( Graywackenitic. ) 



"Slate from the very foot of Homestead island, below the rapids last mentioned [under No. 509]." 

 Ref. Annual Report, x, pages 12, 30, 38. 



