RECENT ADVANCES IN SCIENCE 283 



There is an upper and lower series of basaltic rocks, with an 

 intermediate series of alkaline lavas, a sequence which is 

 paralleled in the Kainozoic volcanic rocks of New South Wales 

 and Victoria. 



In a useful paper on the application of petrological and 

 quantitative methods to stratigraphy (Geol. Mag. (VI), 19 16, 3, 

 105, 163) P. G. H. Boswell shows that detrital mineral assem- 

 blages may be of considerable value for stratigraphical correla- 

 tions within limited areas. For this purpose it is necessary to 

 aim at a knowledge of the mineral and mechanical composition 

 of all sedimentary rocks of the British geological column. A 

 contribution to this knowledge has been made by G. M. Davies, 

 who has determined the mineral constituents of a large number 

 of rocks from the Croydon area (Proc. and Trans. Croydon Nat. 

 Hist, and Scientific Soc. 191 5-6, 53). Conclusions as to the 

 source of supply and conditions of deposition are withheld 

 until more information is forthcoming relating to the com- 

 position of the rocks over a much wider area. 



Mr. B. Smith describes ball or pillow-form structures in the 

 Llandeilo and Bala sandstones of Denbighshire {Geol. Mag. (VI), 

 191 6, 3, 146). These are associated with bucklings and foldings, 

 and are explained as due to the internal readjustments of 

 freshly and unevenly deposited sediments under the control of 

 gravity. 



Economic Geology. — Fluor-spar forms the subject of the 

 fourth report of the Geological Survey on the Mineral Resources 

 of Great Britain. This mineral occurs in greatest abundance 

 in the zinc and lead veins of Derbyshire and Durham. The 

 output for many years has been in excess of home requirements 

 and much fluor has been exported, more than half the pro- 

 duction going to the United States. 



A full description and discussion of Florida phosphates is 

 given by G. C. Matson {Bull. 604, United States Geological Survey, 

 191 5, 10 1 pp.). They are of Tertiary age and of secondary origin, 

 having been redeposited by mechanical or chemical action. 



The sulphur deposits of Sicily are described by W. F. Hunt 

 {Econ. Geol. 191 5, 10, 543). These occur in isolated basin-like 

 areas and are unquestionably sedimentary, as they are inter- 

 calated with thin layers of bituminous salty shales, underlain 

 by tripoli, and covered by massive deposits of gypsum. Hunt 

 believes that the sulphur has been produced by the bacterio- 



