498 Geological Society. 



have moved on as it were without a cause, but also have maintained 

 an incredibly enormous advancing front of many hundred miles in 

 length ! 



Without pretending to offer a complete solution of so difficult a 

 problem, and after stating that many additional and even experi- 

 mental researches are- required in relation to the power of water, 

 drift, and ice, they cannot avoid suggesting as a probable explana- 

 tion of the chief phenomena in the North of Russia, that currents 

 strongly determined in given directions by the elevation of the 

 northern continental masses, might dislodge and set in movement 

 icefloes and detritus, which, grating upon the bottom of a sea, may 

 have produced the parallel striae. They are the more confirmed in 

 this hypothesis, by the fact, that the longer axes of the lakes and 

 stony ridges of Northern Russia have generally the same direction ; 

 so that the supposed icebergs and land detritus would necessarily be 

 borne in that direction. By adopting this view, the existence of the 

 post pleiocene shells of the Vaga and the Dwina, and their relations 

 to the overlying drift from the North, are in harmony ; and whilst 

 admitting so much of the glacial theory as to allow, that in former 

 days glaciers probably advanced further to the South and occupied 

 many insulated tracts, and to a much greater extent than at the 

 present day, the geologist, they conceive, is alone called upon to 

 define and limit the area of land in Scandinavia and Lapland, once 

 covered with solid ice, in doing which he must of course exclude 

 from such agency the vast countries now covered by erratic blocks, 

 which he can demonstrate were deposited upon the bottom of the sea. 

 Angular block-ridges on lake and river Banks. — On the western 

 shore of the great lake of Onega, the attention of the authors was 

 directed, by Colonel Armstrong*, to three parallel ridges of large 

 angular blocks of hard grit (old red sandstone ?), which occur at 

 heights, varying from 20 or SO to 150 feet or more above the level 

 of the water. As these blocks were identical in composition with 

 the solid subjacent rock, and also quite angular, it was at once evi- 

 dent that they had not been drifted, but simply rent from the solid 

 rock which forms that side of the lake. On a first inspection, the 

 authors were disposed to think that these appearances might have 

 been caused by upheaving or vertical shocks of earthquakes, which 

 they presumed might be among the last signs of the great igneous 

 action which had once been so dominant in these northern tracts ; 

 and they were unable to account for them satisfactorily, until they 

 detected the results of modern action of river ice, which completely 

 explained the lacustrine case. 



About 80 miles above Archangel they met with a ridge of large 

 angular blocks of white limestone piled up between the road on 

 which they travelled and the river edge, and about 20 or 30 feet 

 above the stream. Having ascertained that this great river was pe- 

 riodically subject to occasional extraordinary rises in the spring, and 

 that on those occasions it bursts and throws up upon its banks blocks 



* Director of the Imperial Iron Foundries of Petrazowodsk. 



