26 SCIENCE PROGRESS 



occur in intimate association are formed in a lower temperature 

 zone than the bulk of tin deposits free from wolfram. 



J. Coggin Brown and A. M. Heron describe the distribution 

 of ores of tin and tungsten in Burma {Rec. Geol. Surv. India, 

 1919, 50. pt. 2, pp. 101-21). 



In a paper entitled " Notes on Principles of Oil Accumula- 

 tion " {Journ. Geol., 1919, 27, pp. 252-62) A. W. McCoy details 

 important experiments showing that liquid hydrocarbons form 

 in bituminous shales at ordinary temperatures under a pres- 

 sure of 5,000-6,000 lbs. per square inch, applied in such a way 

 that differential movement can take place. Since shales of 

 this character are generally abundant in oil-fields, McCoy 

 believes that oil is produced therein by pressure in areas of 

 local differential movement. Further experiments show that 

 the accumulation of the oil into commercial pools is accom- 

 plished by the agency of capillary water. 



W. F. Jones presents evidence that oil-pools in the Penn- 

 sylvania and Oklahoma fields have only slight and indirect 

 relationships with the tectonic structures of these rocks {Econ. 

 Geol., 1920, 15, pp. 81-7). They appear to be aligned parallel to 

 the extension of ancient shore lines, the sources of supply 

 being lagoonal areas along such coast lines. The present posi- 

 tions and shapes of the pools closely conform to these under- 

 lying or overlying sources of supply, no wide lateral move- 

 ment having taken place. Acceptance of this view has the 

 important practical corollary that oil may be found if drilled 

 for in areas hitherto considered tectonically unsuitable. 



Sedimentary Rocks. — In an interesting paper on the origin of 

 Cretaceous flint W. A. Richardson {Geol. Mag., 1919, pp. 535-47) 

 demonstrates a striking inverse relation between the amounts 

 of silica disseminated through the chalk and that segregated 

 as flint. He further shows that the rhythm of flint deposition 

 has a considerable degree of resemblance to the Liesegang 

 banding. A study of the distribution of flint strongly sup- 

 ports the hypothesis that the substance is due to rhythmic 

 precipitation from solutions diffusing through the chalk at the 

 time of uplift of that formation. 



The chert of the Wreford and Foraker limestones of Kansas 

 and Oklahoma is believed by Twenhofel {Amer. Journ. Sci., 

 1919, 47, pp. 407-29) to be due mainly to the replacement of un- 

 consolidated limestone, the silica being derived from silica in 

 solution which was mingled with the sediments, from silica in 

 solution in the sea water, and from solutions of organic or 

 other silica, or of silicates, deposited with the sediments. 



Another paper by Twenhofel on Pre-Cambrian and Car- 

 boniferous algal deposits in certain American localities (Amer. 

 Journ. Sci., 1919, 48, pp- 339-52) again emphasises the significant 



