298 R. N. Lucas— Geology of. Finland. 



As mentioned above, the hornblende-gneiss is frequently inter- 

 sected by and interbedded with granite to such a degi'ee as to render 

 it difficult to determine which rock is present in the greater quantity. 

 At Mortsjo, one of the many places where this phenomenon occurs, 

 the plainly stratified hornblende-gneiss passes into a fine-grained 

 indistinctly foliated rock, resembling a sy emtio granite. We thus 

 have here a case that is in all probability one of a gneiss meta- 

 morphosed by contact with a granite of similar age to itself, a fact 

 which certainly speaks strongly in favour of the theory that gneiss 

 was originally deposited as such, and has not received its present 

 constitution exclusively through the action of chemical, thermic or 

 mechanical metamorphism. 



Mica, Hornblende, and Actinolite Schists occur at many different 

 places, although not in such a manner in the south and west of the 

 country as to entitle them to be considered as constituting a distinct 

 formation. On the contrary, they form comparatively thin bands 

 interbedded with gneiss, into which they often gradually pass. The 

 mica-schist, the passage of wmich into gneiss is most frequently 

 observed, consists as a rule of black mica and greyish-white quartz. 

 Sometimes, as occurs near Hirvela, thin bands of mica- schist are 

 found alternating with micaceous gneiss, the layers of each rock, 

 however, being sharply separated from each other in such a way as 

 strongly to suggest the sedimentary origin of the whole. More 

 sparingly bands of hornblende-schist have been observed. They 

 consist as a rule principally of hornblende and some black mica, in 

 addition to which red orthoclase and white plagioclase are occasionally 

 though seldom found. The cleavage is generally determined by the 

 mica. The actinolite schists play much the same role as the 

 hornblende schists, which frequently pass into them. Under the 

 microscope they are found to consist in the main of actinolite and 

 quartz, and sometimes contain plagioclase and suggestions of chlorite. 

 Copper ore is frequently to be observed in this rock, and in it occur 

 the celebrated copper deposits of Orijarvi. 



NON-FOLIATED EoCKS. 



Quartzites and Fibrolite Quartzite. — Quartzites occur in consider- 

 able amount throughout the whole district ; seldom, however, 

 independently, but generally interbedded with mica-schist, which 

 by gradual loss of mica frequently passes into it. The quartzite 

 at times seems to form a line of separation between the mica- 

 schists and limestone strata, especially in the neighbourhood of 

 diorite schists, as near Orijarvi, in which situations it is often sand- 

 stony in appearance and fissile. In Tavastland quartzite occurs on 

 a much more extended scale, forming hills of sufficient size to con- 

 stitute conspicuous features in the landscape. Thus, near Turismaa, 

 there is a narrow elevation some three miles in length by one mile and 

 a half in breadth, composed entirely of quartzite striking E. and W. 

 Under the microscope this rock was found to consist almost ex- 

 clusively of quartz, with a thin skin of weathered iron oxide. A 

 light-red mineral — fibrolite — also occurs in small quantities, but is 



