THE ORIGIN OF LAKES. 225 



tan in the western territories of Nortli America, for the 

 deformation of the terraces has been worked out in the 

 case of those lakes, and some of the terraces are actually 

 seen to be cut by fault planes (10). Dr. Gilbert, who 

 described the geology of Lake Bonneville, has also detected 

 proofs of differential movement amongst the old terraces 

 of Lake Ontario, and a number of papers have been pub- 

 lished by Dr. J. W. Spencer, giving accounts of his detailed 

 work on the "warping" or deformation of the terraces 

 around several of the large Canadian lakes of the St. 

 Lawrence Valley, one of which appears in the Journal of the 

 London Geological Society (i\). It may be observed here, 

 that although there is evidence of considerable earth-move- 

 ment having affected the British area since the formation 

 of the principal British lakes, it is doubtful whether any 

 of these lakes owe their origin wholly or in part to this 

 earth-movement, which appears to have been singularly 

 uniform in amount over very wide areas, and therefore to 

 differ from the " warping " movements which have taken 

 place in Canada and the Western Territories. Still it is 

 possible that differential movement has played some part 

 in the formation of some of our lakes, but it will require 

 much more work upon the physical structure of our lake- 

 basins before the partial or entire production of any of them 

 by differential movement can be established or disproved. 



There is one kind of earth-movement due to local 

 causes which must be noticed, as some lake-basins are un- 

 doubtedly produced thereby. I refer to the solution of 

 material underground and the consequent subsidence of 

 overlying rocks. The artificial removal of salt in the New 

 Red Sandstone areas of North-west England and the 

 consequent subsidence of the ground is well known to all, 

 and the removal of limestone may have given rise to some 

 of the smaller lakes that occur in limestone regions in 

 Britain, owing to the falling-in of the roofs of cavernous 

 hollows underground. The Konigsee has been cited by 

 Credner as a lake which was probably formed by the re- 

 moval of soluble matter from beneath it ; and many other 

 instances probably occur. 



