2i 4 SCIENCE PROGRESS 



believes that most occurrences of chert may be satisfactorily 

 explained on the replacement hypothesis. The following 

 features are indicative of replacement : occurrence of chert 

 along fissures and the irregular shape of some chert nodules ; 

 the presence of patches of limestone in some chert masses and 

 the association of chert with silicified fossils ; preservation 

 of structures and textures of other rocks in some cherts ; failure 

 of some chert to follow definite zones in limestone formations ; 

 and the occurrence of silicified oolites. 



Barton, D. C, Notes on the Mississippian Chert of the St. 

 Louis area, Journ. Geol. 191 8, 26, 361-74. 



From a petrological study of the Leicestershire dolomitic 

 limestone, L. M. Parsons arrives at the conclusion that the 

 majority of the rocks are of contemporaneous origin, that is, 

 formed from ordinary limestones by replacement in sea-water 

 at or soon after deposition {Geol. Mag. 191 8, 5, 246-58). They 

 are situated between the more normal Carboniferous Lime- 

 stones of Derbyshire and the Charnwood region of ancient 

 rocks. It is suggested that the dolomitic limestones have 

 been formed in shallow portions of the Carboniferous sea 

 adjacent to the old Charnwood land surface. 



Economic Geology. — Emmons, W. H., The Principles of 

 Economic Geology, 191 8, pp. 506 (McGraw & Hill Book Co.). 



The first part of the Geological Survey Memoir on refractory 

 materials, dealing with the sources and geology of ganisters, 

 silica-rocks, sands for open-hearth furnaces, and dolomite, is 

 now published (Special Reports on the Mineral Resources of 

 Great Britain, vol. vi. Refractory Materials. Mem. Geol. Surv. 

 191 8, pp. 233). The accounts of fireclays and moulding-sands, 

 and the details of the laboratory work on refractories generally, 

 form the subjects of succeeding parts of the memoir. Re- 

 fractory materials of many sorts are abundantly distributed 

 in the British Isles, but their industrial use involves consider- 

 able selection and investigation. 



According to a report by L. Hinxman and M. Macgregor 

 on the distribution and geological position of the valuable 

 fireclays and ganisters of the South of Scotland, the Millstone 

 Grit is the chief source of refractory materials over this region, 

 although they occur in all the remaining subdivisions of the 

 Carboniferous. Large areas are still inadequately prospected 

 for the highly refractory Millstone Grit fireclays. These rocks 



