186 Scientific Intelligence. 



lems of continental origin and maintenance, mountain-building 

 and the nature of the earth's interior. On these subjects the 

 long-felt need has been for facts, and it is for these that the 

 present article is especially valuable. Mr. Hayford has utilized 

 the triangulation and astronomic determinations of latitude and 

 longitude within the United States. The preliminary results of 

 the investigation, which is still in progress, indicate that the 

 most probable value of the limiting depth of isostatic compensa- 

 tion is 71 miles and that it is practically certain that the limiting 

 depth is not less than 50 miles nor more than 100 miles. It is 

 certain that for the United States and adjacent regions, including 

 oceans, the isostatic compensation is more than two-thirds com- 

 plete — perhaps much more. 



Internal variations of specific gravity to the extent of three 

 per cent from the mean, both above and below, will account 

 for the ocean basins and plateaus. As a consequence of this 

 limited zone of isostatic compensation it is pointed out that 

 isostatic adjustment involves a subsurface undertow away from 

 areas of sedimentation and toward areas of erosion : this vis- 

 cous undertow acting as a thrust tending to crumple back the 

 continental margins upon themselves and at least aiding in the 

 formation of mountains. In this connection the reviewer wishes 

 to point out facts not commonly cited, viz.: that Major Dutton 

 perceived as long ago as 1872 the inadequacy of the still 

 popular hypothesis of terrestrial cooling as a sufficient source 

 of mountain-making,* and in 1889 suggested the agency of 

 this lateral undertow.f The efficiency of this agent must 

 depend upon the depth of the compensating zone, its thickness 

 and viscosity. It is doubtful if Mr. Hayford's figures justify ele- 

 vating this factor to a major place, but the present limitation of 

 the zone makes it at least a minor factor, and Dutton's suggestion 

 in this respect must stand as an example of remarkable scientific 

 prevision. J. b. 



2. Pleistoce?ie Deposits of South Carolina; by Griffith 

 Thompson Pugh : A thesis submitted to the Faculty of Van- 

 derbilt University for the Degree of Doctor of Philosophy, 

 Nashville, Tenn., 1905; 74 pp. — This paper is an attempt at 

 ascertaining what must have been the environmental conditions 

 under which lived the Pleistocene mollusca of the state. To 

 that end the species are tabulated, together with the conditions 

 of environment of their living representatives. The conclusion 

 is reached that at least in South Carolina the Pleistocene sea tem- 

 perature, if differing at all from that of the present, was slightly 

 higher rather than slightly lower. The method of detailed and 

 tabulated investigation is excellent and should be followed out 

 for other localities. The reviewer would point out, however, 



* A Criticism upon the Contractional Hypothesis, by Captain C. E. Dutton, 

 U. S. A., this Journal, vol. viii, p. 113. 



f On Some of the Greater Problems of Physical Geology, Phil. Soc. of 

 Washington, vol. xi, pp. 51-64. 



