Reviews — Professor Tllden — Gases in Rocks and Minerals. 177 



ccenencbyma which surrounds the parent calyx, and in which the 

 young calices are opening, can be quite naturally accounted for by 

 the secondary alteration of the primitive costas, an alteration which 

 would necessarily involve the degeneration of the extracalicular 

 portions of the mesenteries. Further, Madrepora and Turhinaria 

 are best explained by deducing them from such a parent polyp by 

 the different relative growths of the parent and its ring of daughters, 

 the primitive epithecal saucer being left behind. In Madrepora the 

 parent shoots up, and somewhat undeveloped daughters spring in. 

 tiers from its sides. In Turhinaria the ring of daughters grows up 

 and forms a cup. The detailed evidence for this line of argument 

 to be deduced from Moutipora will be the subject of a paper 

 which has already been some months in preparation. None of 

 ]\Iiss Ogilvie's arguments on this subject seem to me to have any 

 weight as against this much simpler and more natural reading of the 

 facts. 



The value of the rest of Miss Ogilvie's system must be left to 

 the judgment of those who have worked over the different points. 

 There can be no doubt that long concentration upon, and wide 

 survey of, coral form -variations have given her an insight which 

 her, to my mind, mistaken method cannot wholly vitiate. Her 

 circular arrangements of the families and genera is an excellent 

 device, though one is staggered at the boldness with which she has 

 filled in the details. We may, however, accept these as her 

 suggested provisional arrangement, which further and profounder 

 study of coral variations, with the special object of tracing the lines 

 along which these variations have travelled, will gradually emend, 

 until our common goal has been reached, viz. a natural system 

 of the Madreporaria. 



In the foregoing pages, I have freely criticized Miss Ogilvie's 

 conclusions from my own point of view. But whatever difference 

 of opinion there may be between us as to what conclusions may, 

 and what may not, be justly drawn from the new facts with which 

 she has enriched us, there can be no difference of opinion as to the 

 facts themselves. I am convinced that these will prove invaluable 

 to all students of coral morphology. Henry M. Bkrnard. 



Streatham, S.W. 



II — On the Gases enclosed in Crystalline Eooks and Minerals. 

 By W. A. TiLDEN, D.Sc, F.R.S. Proc. Royal Soc, vol. Ix 

 (1897), p. 453. 



AFTER referring to the fact that many crystallized minerals 

 contain gas enclosed in cavities in which drops of liquid are 

 also frequently visible, the author alludes to his researches on 

 Peterhead granite, which show that when heated in a vacuum, it 

 gives off several times its volume of gas, consisting, to the extent 

 of three-fourths of its bulk, of hydrogen. Since these observa- 

 tions were made Mr. A. W. Wright has obtained hydrogen from 

 a certain " trap " rock in America, and Professor Dewar and 



DECADE IV. VOL. IT. — NO. IV. 12 



