ON THE OBiaiN OF MOUNTAIN RANGES. 



161 



as he oontonds. No such objection can however be taken to 

 the fact that at Durness in the Highlands certain strata liave 

 boon pushed forward bodily over younger rocks for a distance 

 of not less than ton miles. But even granting that his objec- 

 tions to the figures given by Professors Hoim and Claypole 

 have some weight, the discrepance, though it may be some- 

 what reduced, cannot possibly in this way be annihilated. 



A further criticism is suggested by the consideration of 

 the observed contortions in mountain ranges. Mr. Mellard 

 Reade tolls us that "the upper layers of the earth's crust 

 being loss affected by these variations in temperature as the 

 surface is nearcd, are by tlie ridging up thrown into a state 

 of tension" ; -whence arise, as we have seen, gaping cracks 

 along the summits of the anticlinals. How comes it then, 

 we may ask, that the Eocene strata, the latest of the long 

 series of continuous deposits in the Alps, are so wildly con- 

 torted in those mountains ? In our own district the main 

 foldings of Ibo strata took place, I believe, shortly after car- 

 boniferous times; but the fact that the then i-eenntly formed 

 rocks are so folded and ridged is evidence that they were 

 not thrown into a state of tension, but one of compression. 



Another fact does not seem to have been duly weighed by 

 Mr. Reade. If we call into play expansion by the rise of the 

 isogeotherms due to sedimentation, must we not, by parity of 

 reasoning, call into play contraction by the lowering of the 

 isogeotherms due to denudation? The denudation of the 

 Alps has been enormous. Must there not have been a pro- 

 portional lowering of the isogeotherms, and therefore a 

 proportional contraction ? Bnt where is the evidence there- 

 of ? In arguing against a rise of the land, proportional to 

 the lightening oF the burden by subaerial denudation, Mr. 

 Reade says, " It may be pointed out that the removal of 

 30,000 feet of rock from the Uinta Mountains has not been 



