R. N. Lucas — Geology of Finland. 299 



nevertheless present in sufficient amount to give the whole rock 

 a very characteristic appearance. 



Pyrargyllite, hornblende, and tourmaline occur as accidental con- 

 stituents. The fibrolite needles are sometimes clustered together, 

 sometimes arranged radially round a transparent nucleus and usually 

 pierce the quartz. The whole rock has been enormously crushed 

 and sheared, and would seem in every way to resemble closely the 

 quartzite of the " Pfahl " in the Bohmer Wald (described by Gumbel, 

 " Ostbayerische Grenzgebirge "). On its northern side it occurs in 

 contact with a peculiar rock — a kind of quartzite-gneiss or quartzite- 

 breccia, which the microscope shows to be a hornblende-gneiss 

 infiltrated with quartz. It has been thought possible by several 

 geologists that the quartzite of the " Pfahl " may be of eruptive 

 origin. There is much to favour the same opinion being held of the 

 Tavastland quartzite. Among the principal grounds which may be 

 urged in its support, the occurrence of this contact alteration of the 

 surrounding gneiss is certainly of importance. 



Crystalline Limestones. — The crystalline limestones interbedded 

 with the gneiss formation are of considerable interest, both from the 

 regularity with which their strike follows that of the gneisses, 

 from the number of accessory minerals which, as is usual with the 

 Laurentian limestones, they contain, and from the very interesting 

 contact phenomena with granite which they display. The rock is 

 generally coarsely crystalline and of a pure white, though at times 

 it passes into a fine-grained yellowish marble, as near Triiskby. 

 The accessory constituents most usually found include felspar, 

 augite, serpentine, graphite, pyroxene, malakolite, condrodite, and 

 wollastonite. The latter mineral has been observed near Yttela, 

 where the limestone occurs in contact with eurite-gneiss. Most 

 generally the limestones occur completely surrounded by granite. 

 A typical contact presents the following features : — The limestone is 

 coarsely crystalline, and the surface of contact smooth and irregular 

 in outline ; the granite, which is likewise coarse-grained, is covered 

 by a brown talc-like skin, and is completely free from any veins of 

 limestone projecting into it ; the skin intervening between the two 

 permits the limestone to be easily pulled apart from the granite. 

 At times a band, some feet thick, of white oligoclase intervenes 

 between granite and limestone, and the granite shows a disposition 

 towards parallelism of arrangement owing to the occurrence of layers 

 of biotite. Near Kaukelmaa occur some small bands of limestone 

 surrounded by and mixed up with greyish eurite destitute of distinct 

 strike — the whole apparently being a fragment uplifted by granite. 

 The coarsely crystalline structure of the limestone in proximity to 

 the granite (as above described) renders the opinion tenable and 

 even pi*obable that the latter rock has been deposited from hot 

 springs which have found their way up through clefts in the granite 

 from below. Limestones of a similar kind are also found in con- 

 junction with pegmatite in veins penetrating gneiss. 



(To be continued.) 



