42 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



conform to the outline of the dry land opposite to it. May we not 

 then explain these appearances by saying, that as the mass was 

 upheaved from the bed of the ocean, the sides opened, in a degree, 

 wdth the strain and shrank inwards or towards the land, so as to 

 produce (in the case of the channel to the north-east of the Shetlands, 

 the northern entrance of the Irish Channel, and the entrance of the 

 English Channel) a great crack or rent, which opened more and 

 more as the mass rose into shallower water ? This appearance in 

 the last case, at the entrance of the English Channel, can be best 

 studied in Maury's small Chart of the JS'orth Atlantic. 



The relations of the strong projections or angles, and the weaker 

 sides, of the half-hexagonal figure thus described are then treated of 

 by the author ; — the analogous irregularly hexagonal outline of the 

 Isle of Arran and of the Spanish Peninsula, and its 100 -fathom 

 line, — the absence of such a line of angles on the eastern side of 

 England, where the strata are softer, — and the bearings that certain 

 lines drawn across the British Isles from the projecting angles of the 

 polygon appear to have on the strike, and other conditions of the 

 strata — were described. After some remarks on the probable effect 

 that shrinkage of the earth's crust must have on the ejection of 

 molten rock, the author observed that, in his opinion, the action of 

 shrinking is the only one we know of that will aiford any solution 

 of the phenomena treated of in this paper, namely, long lines of 

 depression accompanied by long lines of elevation, often, as in the 

 case of the British Isles, Spain and Portugal, and elsewhere, belong- 

 ing to parts of huge polygons broken up into small ones, as if the 

 surface of the earth had once formed part of a basaltic causeway. 



