218 Dr. C. Callaway — Notes on Metamorphism. 



already indicated, there is no finish to the edges of the cells around 

 the bare spot, which one would naturally have expected had this 

 outer shell layer never extended beyond its present margin. 



I hope the new points of structure here noticed in Eichwaldia , 

 Capeivelli, Dav., will lead to farther examination of this interesting 

 shell by those who have opportunities of examining specimens 

 from various localities, so that our knowledge of both its internal 

 characters and external structure may be extended beyond that now 

 known ; and this can only be done by the discovery and examination 

 of specimens in which the shell-structure has suffered little change 

 through crystallization. 



Note. — Since this paper was written and sent to the Editor of 

 the Geological Magazine, Dr. Davidson has informed me that in 

 his " Supplement to the British Silurian Brachiopoda," p. 141, he 

 had omitted to note, while making reference to what Professors 

 Angelin and Lindstrom had figured and described of the external 

 and internal characters in JEichioaldia Capewelli, Dav., from Swedish 

 specimens in their " Fragmenta Silurica," viz. that they had also in the 

 same work, p. 25, pL ii. fig. 16-20, described and figured two distinct 

 layers in this shell, both of which are perforated by two difierent 

 sets of tubules — an outer layer running obliquely inwards and 

 downwards, and a second or inner layer, in which the tubules per- 

 forate the shell in a horizontal manner from the inner surface. 



This being the case, they have therefore the merit, of having been 

 the first to put upon record the points of structure which I here 

 notice more fully than they have done ; and which I had independ- 

 ently discovered for myself. In the description of Professors Angelin 

 and Lindstrom, they only notice two layers in the thickness of the 

 shell. In my paper, I call attention to a third outer layer, that 

 forms the external hexagonal cells, and which, when present, on per- 

 fect portions of the surface of the shell, conceals the inner or second 

 layer, which is formed of small polygonal cells, as noted in the paper. 



IV. — Notes on Progressive Metamorphism. 

 By C. Callaway, D.Sc. F.G.S. 



ON no branch of geology has there been more imaginative writing 

 than upon metamorphism. Some speculations have, indeed, 

 diverged into the humorous. Keen-eyed observers, with vision 

 capable of piercing through miles of solid rock, have described to us 

 those processes of subterranean cookery by which Pluto has converted 

 sandstones and shales into granite, metamorphic schists and por- 

 phyries. If water was used, the rocks were " stewed " ; if not, 

 they were only " baked " or perhaps " melted." Furthermore, it 

 was declared, and text-books submissively taught, that rocks of 

 almost every epoch have sometimes undergone these mystic changes. 

 In North America, some metamorphic schists were " Triassic " ; 

 while in the European Alps we had granite and gneiss of " Eocene " 

 age. In Britain, men were more moderate, and we were not asked 

 to extend our faith beyond the limits of the Palseozoic formations. 

 The evidence on which these conclusions were advanced was 



