294 R. N. Lucas— Geology of Finland. 



The central lake district, comprised roughly speaking by a polygon 

 drawn through the points Heinola, Tammerfors, Jyvaskyla, Kuopio, 

 and St. Michel, is mainly of eruptive origin, consisting of granites, 

 syenites, etc., of Laurentian age that have pushed their way through 

 the gneisses and schists that surround them, and are very likely to 

 some extent responsible for the tremendous crushing and crumpling 

 which the latter have undergone. The " rapakivi " district of the 

 extreme south, which will be described fully in the sequel, may be 

 regarded as in some sort a continuation of this eruptive area. Eound 

 this region are arranged the foliated members of the Archaean series, 

 contorted, folded, reduplicated and turned upside down to any extent, 

 but still in the main striking with considerable regularity, on the 

 west side, N.— S. or N.E.— S.W. ; on the east side N.W.— S.E. ; 

 and on the south side E. — W. On proceeding to walk outwards, 

 therefore, from this central granitic district, one would successively 

 cross the edges of the Laurentian series, meeting first with the 

 granite-gneiss and then with the younger gneisses and schists, though 

 the exact order in which one would encounter the various members 

 is often confused and inverted by folding or reduplication. In the 

 more eastern districts, Karelen and the country north of Ladoga 

 Lake, one would eventually meet the Huronian, and, further east 

 still, the Taconian series. Of course it is not intended to be under- 

 stood by this that the eruptive rocks are confined to the districts 

 above indicated, the whole of all these series being much pierced 

 by both acid and basic intrusive rocks, but merely that within this 

 region eruptive rocks predominate. It will thus be seen that the 

 geotectonic structure of Finland is not unlike that of Switzerland 

 during the Triassic period — a low Archaean district — composed 

 centrally in the main of granite and allied rocks, towards its 

 outskirts of gneisses and schists, which are overlain by rocks of 

 comparatively recent geological age. Should Finland ever be raised 

 into a great mountain-chain, which, as the country has for a long 

 time been continually rising, may some day be brought to pass, this 

 central granite area, then enormously compressed, would probably 

 take upon it exactly the appearance and characteristics of the 

 protogene granite of the Central Alps, and the gneisses and other 

 members of crystalline and sedimentary series would be found 

 occupying corresponding situations. 



The district to which the following notes principally refer lies to 

 the south of this central granitic region, and comprises consequently 

 the older members of the Archaean series. 



It is proposed to divide the subject into two parts, dealing with — 

 I. Foliated and Crystalline Eocks. II. Eruptive Eocks. 



Foliated Eocks. 



Granite-Gneiss.^ — This is the name now generally adopted by 

 the Finnish geologists for the lowest and consequently the most 



1 Though placed under the heading " Foliated Eocks" granite -gneiss should more 

 properly be described as "banded." 



