614 THE LOWER SILURIAN PERIOD. 



afforded trilobites of the genus Paradoxides. These fossils would 

 indicate a position in the lower part of the Lower Silurian series, 

 possibly on the horizon of the Potsdam sandstone or Lingula flags. 

 If so, the Lower Silurian limestones are either absent or buried by 

 the unconformable superposition of the next series, or of the carbon- 

 iferous beds which in some places immediately adjoin these older rocks. 

 It is to be observed, however, that the mineral character of the rocks 

 themselves very closely resembles that of some portions of the " Quebec 

 group " of Sir William Logan. If coeval with this, they would be 

 somewhat higher in the LoAver Silurian scale ; but I think it may be 

 safely affirmed that no newer group than the Quebec series can claim 

 them with any show of reason. We may therefore in the meantime 

 regard these rocks as probably representative of some portion of the 

 lower part of the Lower Silurian, but without venturing to assign 

 them to any definite horizon, and admitting the possibility that future 

 researches may establish differences sufficient to divide them into 

 distinct formations. More especially in the western part of Nova 

 Scotia, where this band attains to great breadth, I entertain the hope 

 that a continuous sequence may be one day ascertained from the 

 Devonian to the base of the Lower Silurian. 



Large though this district is, there is by no means so great a variety 

 in its rocks as in those of the district last described ; and most of them 

 are nearly related to each other, being composed of the same materials 

 variously arranged. I shall notice them specially with reference to 

 their differences from those of the Upper Silurian series. 



1. Granite, as it occurs in this district, is a crystalline mixture of 

 white, or more rarely flesh-coloured, felspar,* with smoky or white 

 quartz and gray or black mica. It varies in its texture, and is some- 

 times porphyritic ; that is, it consists of a base of fine-grained granite, 

 with large crystals of felspar forming distinct spots. It often contains 

 altered fragments of the neighbouring slates, and penetrates in veins 

 into the adjoining rocks, which in its vicinity are always more highly 

 metamorphosed than usual. 



2. Gneiss is a fine-grained granitic rock, arranged in lamina? or 

 layers. It is unquestionably here, as in the Upper Silurian district, 

 a product of the metamorphism or "baking" of sedimentary rocks 

 by heat and water, and in this series it almost invariably holds mica 

 and not hornblende. 



3. Mica slate consists of quartz and plates of mica, forming a highly 

 fissile rock with shining surfaces, and usually of a gray or silvery 



* Orthoclase, but with soda as well as potash. The granite of Annapolis, mentioned 

 in last chapter, has in some places reddish quartz. 





