Geology and Mineralogy. 309 



Hay and Prieska, with some notes on Herbert and Barkly 

 West, by A. W. Rogers ; Geological Survey of portions of the 

 Divisions of Vryburg and Mafeking, by A. L. Da Toit ; Geologi- 

 cal Survey of the .Divisions of Tulbagh, Ceres and Worcester, by 

 E. H. L. Schwartz; A Raised Beach Deposit near Klein Brak 

 River, by A. W. Rogers. 



These papers are accompanied by illustrations and geological 

 maps, which add much to their effectiveness. While the work is 

 all of the nature of detailed reconnaissance, the survey deserves 

 great credit for the large amount of high grade work done on an 

 appropriation of less than $10,000. New facts are given regard- 

 ing the interesting line of volcanic rocks, both lavas and breccias, 

 which accompany the fault separating the Uitenhage beds from 

 the Zuurberg. Further evidence of glaciation is presented, show- 

 ing a cold climate during the deposition of the Griqua Town 

 beds. 



From the standpoint of the physiographer, the work of Mr. 

 Schwartz on the coastal plateau is of particular interest. Origin 

 of topographical features is discussed somewhat in detail, and the 

 terraces, one submerged, two others at elevations of 700 and 1500 

 feet, respectively, are described. The 700 ft. " uplands coastal 

 plateau," which has been previously described as a peneplain, 

 is now considered to be a plain of marine denudation, and is 

 compared with the similar plains of marine erosion in Europe. 



H. E. G. 



5. Seismic Geology. — Recent geological work on areas of 

 complicated rock structure, taken in connection with a detailed 

 study of earthquake regions, seems likely to result in a change of 

 mental attitude toward dynamic forces. It seems as if the effort 

 to escape the theories of catastrophism in geology had carried us 

 so far in the opposite direction that little room is left in geologi- 

 cal thinking for the undoubted occurrences of sudden dislocations 

 and for the production of topographic forms, other than by the 

 normal processes of erosion. In a recent work on Seismic Geol- 

 ogy by Wm. H. Hobbs,* the necessity for this new view is clearly 

 brought out. The centrum theory for earthquakes seems now to 

 be generally abandoned because only of limited application, and 

 the ordinary cause for earthquakes is to be found in movements 

 of orographic blocks. Professor Hobbs has brought together a 

 number of instances of dislocations of the earth's surface as the 

 result of macroseisms, beginning with the Calabrian earthquake 

 of 1783 and ending with the California earthquake of April 18, 

 1906, — a list which in itself is imposing, but which, undoubtedly, 

 would be much extended if scientific observations had been more 

 generally made. The following generalizations are announced 

 concerning surface dislocations at the time of earthquakes. 



* Some Principles of Seismic Geology, by William Herbert Hobbs, with an 

 Introduction by Eduard Suess. From Gerlands Beitrage zur Geophysik, 

 viii, pp. 219-292, 1 pi. and 10 figs. Leipzig, 1907 (Wilhelm Engelmann). 



Am. Jour. Sqi.— Fourth Series, Vol. XXIII, No. 136. — April, 1907. 

 29, 



