RECENT ADVANCES IN SCIENCE 399 



Natural History of Sedimentary Rocks 



VAN Tuyl, F. M., The Origin of Dolomite, Iowa Geological Survey, Annual 



Report, 1 916, 25, 251-422. 

 NORTON, W. H., A Classification of Breccias, Journ. Geol. 191 7, 25, 160-94. 

 Jeffrey, E. C, Petrified Coals and their Bearing on the Problem of the Origin 



of Coals, Proc. Nat. Acad. Set. Washington, 1917, 3, 206-11. 

 Kindle, E. M , Recent and Fossil Ripple-mark, Geol. Surv. Canada, 1917, Mus. 



Bull. 25, pp. 121. 

 Bucher, W. H., Large Current-ripples as Indicators of Palasogeography, Proc. 



Nat. Acad. Sci. Washington, 191 7, 3, 285-91. 

 Kindle, E. M , Some Factors affecting the Development of Mudcracks, Journ. 



Geol. 191 7, 25, 135-44. 



In his exhaustive monograph on the origin of dolomite, 

 Van Tuyl shows that the great majority of stratified dolomites 

 have been formed by the alteration of limestone. A little 

 dolomite may be a chemical precipitate or of clastic derivation. 

 It is doubtful whether organisms have ever given rise to more 

 than weakly dolomitic limestone, and the importance of marine 

 or surface leaching has been greatly over-emphasised . The most 

 extensive dolomitisation of limestone has been effected under 

 the sea by replacement. Dolomitisation by ground-water is 

 believed to be only local and imperfect. 



Kindle 's work on ripple-mark will become the standard 

 publication on that phenomenon. He elucidates the criteria 

 distinguishing the various kinds of wind, current, and wave 

 ripples ; and has made use of several ingenious methods of 

 studying and securing records of ripple-marks under water. It 

 is shown that fossil ripple-marks may be diagnostic of marine or 

 lacustrine conditions, and that they have considerable palseo- 

 geographic significance. 



MINERALOGY AND CRYSTALLOGRAPHY. By Alexander 

 Scott, M.A., D.Sc, University, Glasgow. 



Anisotropic Liquids. — Since Lehmann's extensive investiga- 

 tions of the doubly refracting liquid obtained by melting 

 cholesteryl benzoate a large number of memoirs on the subject 

 have appeared and many theories propounded to explain the 

 phenomenon. Voigt (Physik. Zeit. 17, pp. 76-87, 128-35, 

 152-61, 19 1 6) summarises the experimental work which has 

 been done and discusses at length these various theories. From 

 a critical consideration of all the investigations of isolated 

 drops and homogeneous layers and of the physical properties 



