1845.] ^01 



only five or six winters ago, at a spot called Cefn-y-Orsidd, where 

 the slope of the mountain ridge is about 15° or 20°, and where 

 numerous blocks fi'ozen together became suddenly disengaged by 

 a thaw, and moving downwards on sheets or sledges of ice, they 

 travelled over a space of nearly 400 yards, and were there checked 

 by the resistance of a wall, part of which, however, was broken 

 through and removed. From these instances, occurring in our own 

 country at a moderate elevation, it will be seen to be possible that 

 boulders, even of considerable size, may be removed without glacial 

 action. 



With regard to the Flynnon Llugwy boulders, therefore, as there 

 appears no evidence of their being due to glacial action, their pre- 

 sence may be better accounted for in some such manner as this. 

 The author concludes by observing concerning them, that they do 

 not, as Dr. Buckland considers, repose on small gravel, except near 

 the river, and where this gravel has been subsequently washed 

 under them. 



April 30. 1845. 



On the Paleozoic Deposits of Scandinavia and the Baltic 

 Provinces of Russia, and their relations to Azoic or more an- 

 cient crystalline Rocks ; with an account of some great features 

 of dislocation and metamorphism along their northern fron- 

 tiers. By Roderick Impet Mukchison, V. P. R. S., V. P. Gr. S., 

 Pres. Roy. Geog. Soc, and Cor. Mem. Inst. Fr. 



The views of my friends, M. de Yerneuil, Count Keyserling, and 

 myself respecting the geological structure of large portions of 

 Russia, particularly in reference to the palseozoic succession of 

 that country, have been already laid before the Society. In those 

 communications allusions were made to the, absence of a well- 

 defined base line for the Silurian rocks of the Baltic and the 

 eastern governments of the empire, owing in some instances to the 

 interposition of arms of the sea, or great interior lakes ; in others, 

 to great masses of detritus, which occupy the surface along the 

 boundary line ; and in others again to the prevalence of eruptive 

 rocks, which have to a great extent nietamorphosed the sedimen- 

 tary masses conterminous with the crystalline rocks of Lapland. 



To remedy, if possible, what would have been serious defects in 

 a work on the structure of Russia wliich is about to be published, 

 and to satisfy myself as to whether the great masses of crystalline 

 rocks which range from Scandinavia over Finland and Lapland, 

 were truly more ancient than any thing to which the term 

 " Silurian " could be applied, or were simply metamorphosed por- 

 tions of the Silurian system, as some geologists had supposed, I 

 last year visited Norway, Sweden, and Finland, and again re- 

 visited St. Petersburg. Having now adopted definite views on 

 this subject, having also completely satisfied myself respecting 

 those tracts which are referable respectively to lower and upper 

 Silurian rocks, and having observed a copious development of old 



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