It. N. Lucas — Geology of Finland. 293 



Fig. 3. Eurycormus grandis, right nasal bone, outer aspect. 



,, 4. left hyomandibular, outer lateral aspect. 



„ 5. anterior section of mandibular ramus, d. dentary. spl. splenial. 



„ 6. posterior end-view of right mandibular ramus, showing gingly- 



moid surface. 



„ 7. two anterior vertebrae, lateral aspect, hyp. hypocentruni. pi. 



pleurocentrum. 



„ 8. front view of dentition of vomers (? and palatines). 



„ 9, 10. Leedsia problematica, A. S. Woodw. ; imperfect gill-rakers, side view. 

 Oxford Clay, Peterborough. [Collection of Alfred N. Leeds, Esq., 

 Eyebury. ] 



10a. edge view of part of Fig. 10. 

 Unless otherwise stated, the Figures are of the natural size. 



III. — Notes on the Geology of Finland. 

 By R. N. Lucas, B.A. 



A STAY in Finland of some months' duration (in the summer of 

 1885) enabled me to make an acquaintance of considerable 

 intimacy with the Archasan rocks of that very interesting district. 



Owing to the kindness of two prominent members of the Finnish 

 Geological Survey, Prof. Wiik, who was good enough to place the 

 valuable collections of the Helsingfors University Museum at my 

 disposal, and was constantly ready to give me assistance in every 

 way, and the Hon. A. F. Tigerstedt, with whom I traversed some 

 hundreds of miles of country, I succeeded in amassing a considerable 

 number of observations, which it was at one time my intention to 

 collect together under the above heading. Since forming this in- 

 tention, however, I had the good fortune to receive the later sheets 

 of the official survey with the accompanying descriptions. I felt 

 that the observations of an individual could in no case possess the 

 value that attaches to an official work of this kind, and I have 

 therefore abandoned my original design. The plan adopted in the 

 following pages has been to replace the observations recorded in 

 my note-book by details drawn from the sheets of the survey. My 

 own observations have merely dictated the general plan, have formed 

 in fact the mould into which the disconnected data drawn from the 

 above-mentioned sources have been poured. Those data themselves 

 have in the main been selected from the survey sheets, and may 

 therefore be regarded as possessing a semi-official stamp. 



An attempt has been made to introduce some uniformity into 

 the nomenclature adopted. Thus " gneissoid granite," " granitoid 

 gneiss," "granitoidite," etc., have been replaced by granite-gneiss 

 and gneiss-granite respectively, — terms to which, as will be seen 

 in the sequel, a very definite signification is attached ; and the con- 

 fusing term " halleflinta " has been relegated to that capacious limbo 

 which has already received the " greenstones " and " traps." 



I. The Arch^an Series. 

 The architectonic relationships of the fundamental rocks of the 

 country, though extremely complicated when viewed in detail, 

 present when considered en masse some general characteristics which 

 may be of use in assisting the reader to comprehend the structure 

 of the region as a whole. 



