RECENT ADVANCES IN SCIENCE 217 



obtain a 21*3 per cent, yield of glycerol in 24 hours. Sup- 

 porting the reduction theory, it was found that a poorer yield 

 was obtained if the solution was thoroughly aerated. It 

 should be stated in conclusion that the amount of glycerol 

 obtained from 100 grams of sugar by Pasteur in 1857 was 

 3-6 grams, while Oppenheimer in 1914 obtained, by means of 

 yeast juice, quantities varying from 3-12 grams. 



GEOLOGY. By G. W. Tyrrell, A.R.C.Sc, F.G.S., University, Glasgow. 



Geological Processes. — In a memoir entitled " Subsidence and 

 Reef-encircled Islands," Prof. W. M. Davis brings forward 

 several independent verifications of Darwin's theory of coral- 

 reefs as upgrowths upon intermittently-subsiding foundations 

 (Bull. Geol. Soc. Amer. 19 18, 29, 489-574). These proofs are: 

 the embayed shore-lines of reef-encircled islands ; the slope 

 of reef-foundations in relation to the physiographic evolution 

 of the islands ; the unconformable contact of elevated reefs 

 with their foundations ; unconformable fringing-reefs at sea- 

 level ; the peculiar distribution of submarine banks in coral 

 seas ; the disappearance of great volumes of detritus from 

 reef-encircled islands ; the absence of reefs from emergent 

 shore-lines ; the unequal depths of lagoons and banks ; and 

 the forms of spur-ends on islands within barrier-reefs. In Prof. 

 Davis's opinion these facts contradict all still-standing theories, 

 and give a decisive superiority to Darwin's. 



The article by the same author in Science Progress (1919, 

 13, 420-44) on the geological aspects of the coral-reef problem, 

 chiefly directs attention to the unconformable contact of reef 

 limestones with their foundations. The evidence thus provided 

 of erosion and subsidence prior to reef formation is strongly in 

 favour of Darwin's theory. 



Foye's observations on Fiji (op. cit. infra) lend support to 

 this view. The earth's crust in this region has been very 

 unstable, and each period of subsidence has been accompanied 

 by reef formation. The elevated reefs rest unconformably 

 upon eroded volcanic foundations. 



Molengraaf has made a notable suggestion to explain the 

 subsidence of volcanic islands around which reefs have grown 

 up (" The Coral Reef Problem and Isostasy," Proc. Akad. Vet. 

 Amsterdam, 191 7, 19, 610-27). He points out that volcanic 



15 



