RECENT ADVANCES IN SCIENCE 475 



cusses the origin of the red partings between the successive 

 basalt flows in Iceland. Microscopic investigation shows that 

 this material is a palagonitic ash, in which the felspar and 

 pyroxene crystals remain perfectly fresh. Mr. Hawkes regards 

 these partings as analogous to the tuff-dust deposits upon the 

 modern lava-deserts of Iceland ; and, instead of indicating 

 a land-surface weathering of long duration, may represent 

 only a few days' accumulation before being sealed up by a fresh 

 lava flow. 



Genesis of Sedimentary Rocks. — A remarkably full and inter- 

 esting paper by Dr. P. G. H. Boswell provides abundant 

 data upon the stratigraphy and especially the petrography of 

 the Lower Eocene rocks of the north-eastern part of the 

 London basin (Quart. Jour. Geol. Soc. 1916, 71, pt. 3, 536). 

 Diagrams showing the isopachyte systems for the London Clay 

 and the Lower London Tertiaries are given, as also many 

 mechanical analyses of the sands, loams, and clays which 

 constitute these deposits. The same author also shows how 

 the mechanical analyses of the North Sea Drift and the Upper 

 Glacial Brick-earths help to distinguish these two series of 

 deposits ("The Petrology of the North Sea Drift," Proc. Geol. 

 Assoc. 1 91 6, 27, 79). The detrital mineral assemblage, how- 

 ever, is the same for each, and is unsurpassed in British sedi- 

 ments for variety and beauty. 



A very complete study of the origin and history of the 

 colouring matter of " red beds " has been made by C. W. 

 Tomlinson (Journ. Geol. 1916, 24, 153, 238), with especial 

 reference to the Permo-Carboniferous and Triassic of the 

 Western United States. He finds that in general the ferru- 

 ginous material was transported and deposited as a mechanical 

 sediment, that changes in oxidation and hydration have 

 been unimportant, and that while " red beds " are not in 

 themselves indicators of aridity, red sediments should bulk 

 more largely in the deposits of arid than of humid regions. 



In a paper on the geological significance of arkose D. C. 

 Barton has tabulated arkose deposits from all over the world 

 with regard to their occurrence and characters (Journ. Geol. 

 1 91 6, 24, 417), and has arrived at the conclusion that arkose 

 can no longer be held to indicate one or two particular sets of 

 rigorous climatic conditions. This rock is laid down whenever 

 a period of deposition is inaugurated over a granitic terrane, 



