174 JS. iV. Lucas — The Older Roclis of Finland. 



(3) Hornblende-gneiss or eurite. This sequence corresponds- with 

 that which has been established by Giimbel in Saxony, by the official 

 survey in Sweden, by Groth in the Central Vosges (Geog. Unt. des 

 Eeichslands), and recently by Prof. Bonney in Switzerland. A 

 similar sequence does not as yet appear to have been established 

 among the Archaean rocks of the British Isles ; but this may be due 

 to local causes or to its having hitherto escaped the notice of 

 geologists. 



2. That the Archaean rocks of Finland present a similarity — I 

 might I think almost say identity — of structure and composition 

 with those of all true Archaean territories, whether situated in 

 Switzerland or Scandinavia, Canada or Saxony. 



3. That though we meet with numerous instances of gneisses 

 ■which have been crushed and contorted, we also find plenty of 

 examples which show no evidence of excessive pressure, and are 

 nevertheless in all respects typical gneisses. This is particularly 

 the case with regard to granite-gneiss and hornblende-gneiss. 



4. That many, if not all, of the crystalline limestones which occur 

 apparently interbedded with granite and gneiss, and in some of 

 which "Eozoon Canadense " was formerly asserted to occur, are not 

 deposits but veins, and are properly speaking to be classed with 

 pegmatites and metallic lodes.^ 



Such are, I think, the principal conclusions to which a careful 

 examination of the Finnish Archaean rocks conducts. They may, I 

 trust, prove of interest not only because they summarize the results 

 of research in a distant countrj'^, but also because, owing to the 

 similarity of the Archaean system at all points where it has been 

 observed, they may be regarded without hesitation as applicable 

 beyond the limits of the district from the study of which they have, 

 in the first instance, been derived. 



Eruptive Eooks. 



In my former article I massed both foliated and eruptive rocks 

 together under the general heading of Archaean. This procedure is 

 both convenient and customary, but it must be understood that its 

 adoption involves the making of assumptions only some of which 

 are in accordance with facts, others being actually controverted by 

 them. Thus to regard the crushed and foliated granites which are 

 interbedded with the older gneisses as of similar age with those 

 gneisses themselves is a view which, as far as I am aware, there is 

 nothing to disprove. But to consider all the eruptive rocks which 

 pierce the gneiss formation as of Laurentian or even Archaean age, 

 is an opinion which it seems to me there is not only nothing to 

 support, but even the strongest presumptive evidence to disprove. 

 Examples of this are afibrded by the rapakivi, which in Southern 

 and Western Finland occurs penetrating older strata, and might, if 

 it had only been observed in those two districts, be regarded as of 



1 Instances in point are afforded by the limestones of Hoponsuo and Henriksnas, 

 in wliicli the Eussian geologist Pusirewski— one of the worshippers of "Eozoon" 

 ■ — formerly believed himself to have discovered the object of his adoration ! 



