132 MIDDLEMISS: PHYSICAL GEOLOGY OF SUB-HIMALAYA, 



M An almost infinitesimal change of bulk, if the mass be large enough, 

 " would explain what to our eyes seem stupendous movements." The 

 author here asks for a great assumption, and one which, if granted, 

 gives the necessary power to upheave as well as to depress. Change of 

 volume by change of temperature is all that is wanted to account for 

 the excrescences of the earth 's crust which eventually form into moun- 

 tain ranges. Where therefore, along with the assumption, is the neces- 

 sity for the cumbrous machinery of great sedimentation, and rise of 

 the isogeotherms, which the author makes the chief point in his argu- 

 ment ? Even supposing great sedimentation had the enormous effect 

 which the author advocates, it must cease to act when the sea level 

 is attained. When, therefore, sedimentation has ceased, where is 

 the power to urge those horizontal sedimentaries into the mountain- 

 ous form ? When they have attained the form of shoals or sand- 

 banks, no further deposition can go on, and therefore (by the author's 

 supposition that sedimentation is the great cause of upheaval) the 

 isogeotherms would cease to rise, expansion of the lower beds 

 would remain as it was, and there would be no further development 

 of mountain-building forces. I see no way out of this difficulty 

 unless it be by the rather grotesque assertion that mountains must 

 therefore be formed subterraneously : a subterranean mountain, how- 

 ever, is somewhat of a contradiction in terms. I regard, therefore, 

 this theory, that great sedimentation is the cause of mountain up- 

 heaval, as incompetent and self-contradictory. 



Though it is like beating a corpse to say more, there is one 

 simple way of refuting the theory which I may indicate. A thickness 

 of eight miles of Cambrian and Silurian strata is urged by the author 1 

 as the sedimentation which brought about the upheaval of the moun- 

 tains of Wales. Now, if eight miles of rock produced this effect, 

 surely half that amount, or four miles, must have had an effect in 

 some proportion ; therefore, when four miles were laid down there 

 ought to have been a mountain range asserting itself, not so high a 

 one perhaps, but sufficient to stop all further sedimentation in that 



1 P. 30. 

 ( 190 ) 



