Geology and Natural History. 93 



showed further that the variations in density which are expressed 

 by the surface relief occur within a hundred miles of the surface; 

 the most probable value, on the assumption that the compensation 

 is complete and uniformly distributed, being seventy-six miles. 

 This conclusion enabled the influence to be computed of these 

 variations of density upon the intensity of gravity at the earth's 

 surface. The present work embraces the results of such an inves- 

 tigation, utilizing 89 stations in the United States and 16 selected 

 stations not in the United States. For each station the whole 

 earth's surface was divided into 31*7 compartments. Then the 

 influence of the topography and the corresponding subsurface 

 density, on the assumption of complete compensation, was com- 

 puted for each compartment. The outstanding difference between 

 the computed and observed values of gravity are known as the 

 " new method anomalies " and are much smaller than the anom- 

 alies computed by previous methods. Thus the results confirm 

 and supplement those of the studies on the deflection of the plumb- 

 line. Together the two kinds of evidence locate ten areas within 

 the United States of excess or deficiency of subsurface mass with 

 reasonable certainty (see plate 19). There is little hope, however, 

 of determining by the use of gravity observations the manner of 

 the distribution of the isostatic compensation with regard to depth. 



J. B. 



2. New Zealand Department of Mines, Geological Survey 

 Branch ; P. G. Morgan, Director. Bidletin No. 18 (New Ser.), 

 The Geology of the Greymoulh Subdivision, North Westland / 

 by Percy Gates Morgan. Pp. viii, 159 ; with 6 plates, 9 dia- 

 grams, 8 maps, 3 geological sections. Wellington, 1911. — The 

 fact that half of the population of Greymouth is engaged in gold 

 and coal (Eocene) mining justifies the extensive treatment of these 

 industries in a geologic report of that district (pp. 15-30, 82-150). 

 The area includes, however, much of interest in addition to its 

 economic development. The description of an ancient coastal plain 

 (upper Miocene in age), built of river gravels and glacial debris 

 as well as of marine clays and sandstones and marked by raised 

 beaches, furnishes additional data on a complex physiographic 

 feature which appears to be coextensive with the Islands. The 

 entire district has been glaciated and presents typical lakes and 

 moraine deposits. The geological column includes argillites of 

 Paleozoic (period undetermined) age, sediments of Eocene, Mio- 

 cene, Pliocene, and Pleistocene periods, with intrusive basic and 

 granitic masses of pre-Tertiary age. During the Paleozoic and 

 Mesozoic the island " was part of or adjoined a continental area," 

 and an extensive uplift at the close of the Mesozoic gave New 

 Zealand continental dimensions. The author of the Greymouth 

 report succeeds Dr. Bell as Director of the New Zealand Geolog- 

 ical Survey, and it is gratifying to note that the high standard 

 of scientific work, as well as the excellence of published maps and 

 reports, set by the Survey is to be maintained. h. e. g. 



