O. F. Harris — Journey through Russia. II 



name, is called gneiss or "granitic schist," and the same class of 

 rock extends for many a square mile around, relieved only by 

 considerable extensions of overlying Glacial and Post-Glacial clays, 

 and sands. The gneiss is believed to be of Archaean age. It is an 

 indescribable mixture, the so-called foliations resembling flow- 

 structure, leading one to the belief that the whole was due to contact 

 metamorphism. In certain cases, where schistose fragments appear 

 to have been more or less absorbed, such an explanation is highly 

 probable ; but, except the " Kapakivi," practically all the granite of 

 South Finland, for at least 200 square miles, is foliated or 

 "gneissose," or "schistose." Over large tracts appearances are 

 certainly in favour of diflerential movements in the magma. But 

 I will not say much about the rock, for our opportunities of 

 examining it in the field were very small. The islets which add so 

 much to the beauty of the environs of the Finnish capital are 

 constituted either of this gneiss or the " gneissose granite." 



The courteous Director of the Geological Commission of Finland, 

 Mr. J. J. Sederholm, invited us all to the offices of the Survey, 

 where he had prepared a representative collection of rocks and 

 minerals, and examples of such fossils (all Quaternary) as have 

 been found in the country. Sederholm's contributions to geology 

 are already important. Amongst other things he has prepared 

 a small geological map of Finland in two editions — solid and drift. 

 He has especially studied the " Eapakivi " ^ and Archaean ^ rocks 

 of South Finland. During the past year or two he has been 

 engaged on the detailed mapping of the extremely interesting 

 country in the neighbourhood of Tammerfors.^ In conjunction 

 with W. Earasay, he prepared the useful guide ^ for the use of 

 members attending the Finland excursion. 



The collection of specimens at the office of the Geological Com- 

 mission proved very interesting, and, in a measure, served as an 

 illustrated guide to the class of rocks which we were to study in the 

 field during the following week. Many types, however, did not lie 

 along our track ; amongst these latter were marvellous examples of 

 " rapakivi " and some "globular" granites, and a word or two 

 respecting them may not be out of place. 



The peculiar kind of " granite " known as rapakivi has, typically, 

 a number of large phenocrysts, commonly rounded or ovoid, com- 

 posed of a kernel of orthoclase enclosed within an envelope of 

 oligoclase (Fig. 1). The rock between these phenocrysts is fine- 

 grained and frequently micropegmatitic. The formation of the acid 



' ' ' TJeber die finnlandisclien Eapakiwigesteine ' ' : Tscherm. Min. und Petrogr. 

 Mitth. Wien, Bd. sii, 1891. 



- " Archiiische Eniptivgesteine a. d. sudwestlichen Finnland " : id., Bd. xii, 

 1891. " Ueber einen metamorph. pracamb. Qiiarzporphyr von Karvia, Proyinz 

 Abo" : Bull. Comm. Geol. Finlande, No. 2, 1896; etc. 



3 "Arcbaiscbe Sedinientformation im siidwest. Finnland": Bull. Comm. Geol. 

 Finlande, No. 6, 1897. 



* " Guide des excursions VII Congres Geol. Intemat. : XIII, Les Excursions en 

 Finlande"; St. Petersbourg, 1897. 



