222 SCIENCE PROGRESS 



of urinary calculi and the formation of concrements, and are 

 applied in a brief survey of the literature of oolitic and spheru- 

 litic structures. 



A similar view is adopted by W. A. Tarr in discussing the 

 origin of siliceous oolites in some Triassic shales of Wyoming 

 (Bull. Geol. Soc. Amer. 191 8, 29, 587-600). He regards the 

 oolites as due to direct precipitation of colloidal silica in shallow, 

 agitated, muddy water. The precipitation is ascribed to the 

 electrolytic and saline character of the water, the resulting 

 siliceous gel aggregating into oolites which were buried as the 

 silts and sands accumulated. 



Since De Geer's classic work in Sweden, the problem of 

 rhythmic banding in the clays associated with glacial deposits, 

 and its bearing on geochronology, has been much discussed. 

 R. W. Sayles has recently made a general survey of the 

 phenomenon in especial connection with the banded glacial 

 clays of the Connecticut Valley and Rhode Island (" Seasonal 

 Deposition in Aqueo-Glacial Sediments," Mem. Mus. Comp. 

 Zool., Harvard, 1919, 47, No. 1, pp. 67, 16 plates). As a result 

 of this study the theory that each pair of alternately coarser 

 and finer sediments represents the seasonal deposits of a year, 

 is placed in a strong position. In the Boston region there is 

 a formation of ":illites and associated slates of Permian age. 

 The slates show fine seasonal banding, and offer extraordinary 

 resemblances to selected specimens of the Pleistocene banded 

 clays, as is illustrated in several magnificent plates. Even 

 the crumpling of layers by the grounding of icebergs, or the re- 

 advance of an ice-sheet, is duplicated in the older formation. 

 These phenomena are shown to occur in the argillaceous sedi- 

 ments accompanying ancient tillites in many parts of the 

 world. 



The following are additional references to new work : 



Gregory, H. E. (Editor), Military Geology and Topography, pp. 281, 117 Figs. 



Prepared and issued under the auspices of the Division of Geology and 



Geography, National Research Council (U.S.A.), 1918. 

 Adams, F. D., Experiment in Geology (Presidential Address), Bull. Amer, 



Geol. Soc. 1 91 8, 29, 167-86. 

 Oldham, R. D., The Interior of the Earth, Geol. Mag., 1919, 18-27. 

 Davis, W. M., Fringing Reefs of the Philippine Islands, Proc. Nat. Acad. Sci. 



1918, 4, 197-204. 

 Ekblaw, W. E., Importance of Nivation as an Erosive Factor, and of Soil Flow 



as a Transporting Agency, in Northern Greenland, Ibid. 288-93. 

 Sapper, K., Geschwistervulkane in Guatemala, Zeitsch. f. Vulc. 1918, 4, 1-14. 



