REVIEWS 191 



The evidence of the striations indicates a general movement of the ice 

 from northeast to southwest. The Ecca or Beaufort series, consisting 

 of fifteen hundred feet of sandstone and shale, occupies most of the 

 surface, while the Stormberg series is found along the eastern border. 



The whole area of Orangia has been intruded by a network of basic 

 dikes and sills of nearly the same composition, and at a later date by 

 the veinlike pipes and dikes of the diamond-bearing rock. This rock, 

 which is known as Kimberlite, has a wide distribution in Orangia, fill- 

 ing both narrow fissures and vents or pipes. Its nature is as yet imper- 

 fectly known, some occurrences giving the impression of a consolidated 

 igneous rock, others being apparently purely fragmental. The author 

 thinks that the typical fissure Kimberlite is a magmatic intrusion, and 

 that the pipes were originally filled, perhaps on more than one occasion, 

 with a magma, which, except near the depth of origin, must have had 

 a very low temperature for an igneous extrusion and which, after solidi- 

 fication, was smashed up by frequently repeated explosions. 



E. R. L. 



The Slates of Arkansas. By A. H. Purdue, with a Bibliography 

 of the Geology of Arkansas by J. C. Branner. Geological 

 Survey of Arkansas, 1909. Pp. 164. 



The part of this volume which is of greatest general interest is chap, 

 iii, which deals with the geology of the slate area. This area includes 

 the part of the Ouachita Mountains from Little Rock westward for 

 about one hundred miles. The sedimentary rocks of known age are of 

 Ordovician and Carboniferous (Pennsylvanian) age, with rocks of 

 unknown age both above and below the Ordovician. 



Above the rocks of known Ordovician age is a group of three forma- 

 tions of which the well-known Arkansas novaculite is the middle mem- 

 ber. In a former publication of the Survey these were all classed as 

 Ordovician, but the author finds no proof of this and thinks that they 

 may be Ordovician, Silurian, or Carboniferous. 



The region is one of intense folding, and thrust faulting is quite 

 common. E. R. L. 



Geological Survey of Georgia. Bull. No. 23, "Mineral Resources." 



By S. W. McCallie, State Geologist. Pp. 208. 



The introductory chapter on the geology of the state is brief and 



presents no new facts. The descriptions of the mineral deposits are 



arranged alphabetically, the general distribution, the mode of occur- 



