2ao 



Common HocJcs of the British Provinces, 



is not slaty, it correspouds in character -with the greenstones of the trr*p 

 family, and lias been called primitive greenstone. It may be termed horn- 

 blende rock. Some of tl'8se horubleudic masses may really have been 

 volcanic rocks which have since assumed a more crystalline or metamorpliic 

 texture. 



" Mica-schisty or Micaceous schist, is next to gneiss, one of the most 

 abimdant rocks of the metamorpliic series. It is slaty, essentially composed 

 of mica and quartz, the mica sometimes appearing to constitute the whole 

 mass. Beds of pure quartz also occur in this formation. In some districts 

 garnets in regular twelve sided crystels form an integrant part of mica schist. 



The great bulk of the Laureutian rocks consists of the above three 

 species Syenitic gneiss, Hernblende schist, and Mica schist. 



But in addition to these, the formation also includes many beds of white 

 limestone, a rock identical in composition with the white marble, so much 

 used for tombstones and other purposes in Canada and the neighbouring 

 States. The white limestone is iuterstratified with the syenitic, gneiss, and 

 other rocks. In some localities there may be seen hills of rock composed of 

 beds of the limestone and syenitic gneiss, alternating with each other through 

 a great thickness of strata. Sometimes there will be a single layer of lime- 

 stone then a stratum of gneiss, then another of limestone, and so on for many 

 yards in depth ; but usually from twelve feet to several hundred feet in thick- 

 ness of each deposit is found without any intermixture of the other. 



The limestone is usually white, but often striped with grey bands. It 

 is also at times somewhat reddish or flesh coloured, and frequently, as do many of 

 the Laurentiau rocks, contains crystals of other minerals. Of these, we shall, 

 in some future article, give more full particulars. 



The following wood cuts are intended to exhibit the manner in whieh 

 the above mentioned rocks underlie the Silurian and higher formations in 

 Canada. 



Sectio7i from North to South across the River Ottawa, East of the City 



of Ottawa. 

 A geological section shews the structure of the earth's crust in any 

 particular place where the section will apply to a certain depth. In the 

 above section the structure of the country on the Ottawa river lying on both 

 shores of the stream, and to the depth of nearly a mile, is intended to be 

 shewn. The black mass at the figure 1 represents the ridge of low rocky 

 hills usually seen near the north shore of the river. They consist in general 

 of Syentic gniess iuterstratified with white crystalline limestone extending 

 southwardly at a lower level under the Silurian rocks which repose upon 

 them in following order. 1st. The Potsdom Sandstone represented by the 

 dotted baud lying above black. 2nd. The Calciferous Sandrock shewn by 

 tlie lowest of the thi-ee bands, with the upright joints. 3rd. The Chazy 



