REVIEWS 163 



strata of New South Wales are now divided into a lower division of marine 

 origin (Burindi series) and an upper division of terrestrial origin (Kuttung 

 series). In the area immediately north of the Lower Hunter River 

 district these have a total thickness of 14,200 feet. Of especial signifi- 

 cance are the glacial tillites and varve shales in the upper portion of the 

 Kuttung series. At least three periods of tilKte deposition occurred in 

 the Seaham district; these are separated from one another by two 

 relatively interglacial epochs during which varve shales were deposited 

 in lakes along the margin of an extensive ice front. Further study is 

 bringing to light the fact that the Australian glaciation near the close 

 of the Paleozoic was not confined to the Permo-Carboniferous period, 

 as that is now defined in Australia, but occurred also in the Carboniferous. 

 In the second edition of this work, no mention was made of glaciation 

 in the Carboniferous period. 



Following the Carboniferous is the very remarkable Permo- 

 Carboniferous period which presents so many problems of extraordinary 

 interest in Australia. Attaining a maximum thickness of 17,700 feet 

 in New South Wales, the Permo-Carboniferous strata comprise an 

 unusual alternation of thick marine series, extensive coal measures, and 

 glacial beds. This period rightly enough has received more extended 

 treatment than any other. 



The book is well printed and well illustrated and gives in concise 



form just what one wishes to know. 



R. T. C. 



The Rift Valleys and the Geology of East Africa. By J. W. Gregory. 

 Pp. 479, pis. 20, figs. 44. Seeley, Service & Co., Ltd., London, 

 1921. 



In this work Professor Gregory has assembled much of what is 

 known of the geology of a very significant portion of the African continent. 

 As the title indicates, the outstanding feature is the Great Rift Valley, 

 or zones of rifting, in which essentially parallel fracturing has taken place 

 on a vast scale. In East Africa the main fault trench, about 40 miles 

 wide, is bordered by prominent boundary faults which in some places 

 form steep single scarps and in some other places cause a succession of 

 steps. On the floor of the trench a great number of lesser faults run 

 nearly north and south approximately parallel to the master bordering 

 fractures. Lakes abound on the floor of the trench. 



The chief value of the book in the opinion of the reviewer lies in its 

 descriptive geology, for one may well receive the assigned cause of the 



