Geology and Mineralogy. 489 



mineral industry of the state by the State Geologist. The total 

 value in 1911 amounted to $37,700,000, with clay and allied prod- 

 ucts first at nearly $19,000,000, zinc mining at nearly $9,000,000, 

 and the Portland cement at $3,260,000. 



11. On the Origin of the Himalaya Mountains, a Considera- 

 tion of the Geodetic Evidence ; by Colonel S. G. Burkard, 

 C.S.I., R.E., F.R.S., Surveyor General of India. Professional 

 Paper, No. 12, Survey of India, Calcutta, 1912. Pp. 25, pis. II.— 

 In this paper the facts regarding the density of the subcrust 

 beneath the several regions of northern India are concisely 

 summed up, and the arguments throughout are clear and terse, 

 which explains the apparent brevity of the paper. The most sig- 

 nificant fact from the author's standpoint is the existence of a 

 narrow subcrustal zone of remarkable deficiency of density skirt- 

 ing the southern base of the Himalayas. Between two stations 

 twenty-five miles apart the deflection changes 45". The change 

 calculated from the uncompensated topographic features would 

 be but 25". On Hayford's hypothesis of isostasy it would be but 

 15". The actual change thus gives remarkably large and unex- 

 plained residuals. It is shown that this cannot be explained from 

 the lighter specific gravity of the trough of alluvium which lies 

 in front of the mountains unless this were enormously deep. It 

 is also shown that a horizontal displacement of compensation 

 within a depth of seventy-six miles does not explain it. 



Colonel Burrard then advances the hypothesis of a great sub- 

 terranean rift. He considers that the subcrustal shell has 

 cracked ; the northern portion, beneath the Himalayas, has shrunk 

 and in so doing has wrinkled the upper crust, at the same time 

 leaving a profound crack on the south which has become filled 

 with alluvium. In comment it may be said by the reviewer that 

 if the crack be assumed deep enough and the alluvium retains 

 its light surface density to an indefinite depth such a hypothesis 

 would explain the deficiency of mass, but it involves a mode of 

 operation which is more difficult to account for and more in unex- 

 plained opposition with the conclusions regarding the deeper 

 crust than is the fact of the deficiency of mass. It involves hori- 

 zontal tension under the northern side of the Indo-Gangetic 

 plain, enormous horizontal compression immediately north with- 

 out adequate mechanical explanation, an absence of consolidation 

 of sediment with depth and a volume of sediment which is 

 unexplained. It seems to the reviewer, therefore, that although 

 Colonel Burrard has made an admirable statement of geodetic 

 facts, his explanation is wholly undemonstrated from the geo- 

 logic standpoint. The possibilities do not seem to be exhausted 

 in the several hypotheses stated and the remarkable distribution 

 of underground densities, to the knowledge of which Colonel 

 Burrard has contributed, offers an inviting field for investigators. 



J. B. 



12. Rocks and their Origins ; by Grenville A. J. Cole, Pro- 

 fessor of Geology in the Royal College of Science for Ireland. 



