RECENT ADVANCES IN SCIENCE 27 



part taken by calcareous algae in limestone formation. Twen- 

 hofel introduces the term ccenoplase for the incrusting or 

 laminated calcareous structures precipitated by algae. 



In a paper on the gypsum-breccia of Chellaston (Derbyshire), 

 Bernard Smith shows that the gypsum was laid down in its 

 present position as such, and has suffered no appreciable 

 alteration or addition since its original deposition {Quart. Jonrn. 

 Geo.Soc, 1919, 74, pt.3, pp.173-203). There is no evidence that 

 the rock was ever anhydrous. When anhydrite is present, the 

 evidence favours the view that it, too, is an original mineral, 

 deposited in the same manner as, and in sequence with, gyp- 

 sum. The brecciation of the Chellaston gypsum is due to the 

 instability of the cover overlying isolated masses of soft gypsum 

 which fill hollows in the Keuper Marl. 



H. A. Baker has studied the petrography of the pebbles of 

 quartzite and siliceous flint-conglomerate in the Oldhaven 

 pebble-beds of the London Basin {Geol. Mag., 1920, pp. 62-70), 

 and has arrived at the conclusion that they are rolled fragments 

 of sarsen and pudding-stone derived from the Woolwich and 

 Reading beds. 



A study of the pebbles of the Middle Bunter Sandstones of 

 the Liverpool district has been made by T. A. Jones {Proc. 

 Liverpool Geol. Sac, 1920, 12, pp. 201-308). The varied assem- 

 blage has considerable resemblance to that of the Midland beds 

 of the same age. A distinctive group of tourmaliniferous rocks 

 points to derivation of the material from a southern or south- 

 western source. This view is supported by the discovery of a 

 pebble with Ordovician fossils within the district. 



Metamorphism and Metamorphic Rocks. — Dr. A. Marker's 

 Anniversary Address as President of the Geological Society 

 {Quart. Journ. Geol. Soc, 1919, 74, pt. i, pp. Ixiii-lxxx) is an 

 illuminating study of the process of metamorphism under the 

 title, " Present Position and Outlook of the Study of Meta- 

 morphism in Rock Masses." Metamorphism, defined as the 

 response in rocks to changed conditions of temperature 

 and stress, is treated throughout as a problem in physical 

 chemistry, which involves the application of the phase rule and 

 the conception of equilibrium. Shearing stress is regarded 

 as a factor of importance co-ordinate vv^ith temperature in 

 governing mineralogical changes in solid rocks. It favours 

 the production of a characteristic suite of minerals, sericite, 

 chlorite, albite, the epidote-zoisite group, amphiboles, etc., 

 as opposed to such minerals as anorthite, potash felspar, 

 augite, olivine, and andalusite, which are products of thermal 

 metamorphism, wherein the dynamic element has been sub- 

 ordinate or absent. These groups are designated as stress and 

 anti-stress minerals respectively. 



