GEOLOGY. 



SECTION A. GEOLOGICAL FORMATION. 



OF the geological formations of Finland Dr Ignatius 

 writes : ' They carry us back to the primitive geological 

 epochs. They are composed in great part of crystalline 

 rocks covered with a comparatively thin layer of earth of 

 the post-tertiary period. With regard to their origin, 

 these crystalline rocks are, some of them, schistose and 

 metamorphic, the others compact and igneous. These are 

 for the most part of the old Taurentian formation. The 

 second, having been erupted from subterranean sources, 

 have traversed the former, turning them over, and covering 

 them in some places over an immense extent of surface. 

 It is these igneous rocks also which form the greatest part 

 of the mountains of Finland. They are divisible according 

 to age, into three principal groups characterised by differ- 

 ent granitic formations granite-gneiss, predominating 

 to the south of Salpauselka ; porphyritic-granite, covering 

 wide extents, especially in the centre of the country; arid 

 pegmatite-granite, which, in the form of thiujllans (of quartz, 

 and of granite, of fine and of coarse grain), are met with 

 in all the other rocks, metamorphic and plutonic. Amongst 

 the granite-porphyroids may be specified one form which 

 the Finnish call Rapakivi, which is well known from the 

 facility with which it is crumbled ; it is found especially 

 to the south of Salpauselka, in a limited space, bounded 

 on the west by a line drawn from Borga to the lake of 

 Paijanne, and on the east by the Vuoksi and the 

 Aeyrapaanselka, a chain of hills which runs from_ the 



B 



