488 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



into hard siliceous and quartzose rocks. These facts, and 

 the coincidence of the form of the lakes with the outlines of the 

 land, as determined by eruptive forces, led me to conclude that 

 the one had been produced at the same time as the other ; or in 

 other words, that the extravasation of so much igneous matter, or 

 in its absence the upheaval of so much of the solid strata, had 

 occasioned corresponding lateral and parallel depressions. This 

 idea is supported by a general review of all the phenomena along 

 the great frontier line in question, the whole of which afford, I 

 think, a striking confirmation, and, on a very grand scale, of the 

 theory worked out by Mr. Hopkins in the British Isles, from the 

 close examination of smaller areas. 



In the first place it is clearly determined by the general strike 

 or bearing of the older palaeozoic deposits and the boundary 

 which they form with the Azoic rocks on the one side, and with 

 overlying systems on the other, that the great line of their up- 

 heaval has been from S. W. to N. E., or rather, more correctly 

 speaking, that they occupy a portion of a grand curve which has 

 accommodated itself to the subjacent crystalline mass on which 

 their lower edges rest — the direction of the Gulf of Finland being 

 from W.S.W. to E.N.E., and that of the White Sea from S.W. to 

 N. E. To this line so defined, the Silurian, Devonian and Car- 

 boniferous deposits strictly conform. The longitudinal upheaval 

 of these deposits has, I conceive, been the chief original cause of 

 the formation of the Gulf of Finland and the channel of the 

 White Sea. These great depressions have been, in fact, produced 

 along the line of junction of the sedimentary deposits with the 

 crystalline rocks, or just where we might look for a physical 

 separation at that period when the crust of the earth was sub- 

 jected to great movements. Now, according to the mathematical 

 demonstrations of Mr. Hopkins, no great portions of the solid 

 crust of the globe could be upheaved without being accompanied 

 or followed by great transverse rents; just such as those that 

 appear at so many intervals along the line we are considering. 

 And if, as we may believe, the original elevation was due to the 

 expansive power of intense heat, and gases struggling to reach the 

 surface, so may we well imagine that where the action was the 

 most powerful, and the cracks the deepest, such action would give 

 vent to linear bands of molten matter that would rise up and 

 form ridges similar to those accompanying the transverse Russian 

 lakes. I was strongly confirmed in the adoption of this view by 

 my last excursion to St. Petersburg. The Gulf of Finland it- 

 self exhibits clear evidences of emission of plutonic matter trans- 

 verse to its chief axis in four small isles, composed of porphyry 

 and greenstone rocks ; for though these isles trend on the whole 

 parallel to the axis of the gulf, or from W.S.W. to E.N.E., the 

 rocks, of which they are severally composed, have been erupted 

 athwart this line, or from N.N.W. to S. S. E. This is best ex- 

 bited in the chief of these islands, called Hochland, which, rising to 

 a height of about 600 feet above the sea, and stretching for a few 



