Dr. C. Callaway—-Rock-Metamorphism. 535 
Tl.—On tHE Conversion oF CHtLorite into Brotirze IN Rock- 
MerraAMORPHISM. 
By Cuarztes Cannaway, D.Sc., M.A., F.G.S. 
[* a paper! read before the Geological Society of London, in 1889, 
I contended that the biotite of the gneisses and schists of 
Malvern had been produced out of hornblende through the inter- 
mediate form of chlorite. As this mineral change is of capital 
importance in explaining the origin of the Malvern schists, ] made 
it one of the principal topics of the paper, and I trusted that the 
evidence I offered in support of it would be considered adequate. 
The further communication on the Malvern rocks, which J read on 
April 26th of the present year, assumed the adequacy of this proof. 
I found, however, that in certain quarters some scepticism on the 
point still existed, and it was suggested that I had overlooked some 
of the chemical difficulties which seemed to forbid the acceptance 
of my view. I therefore crave permission to reply to this objection 
in these pages; and I desire, at the same time, to point out that 
since the reading of my paper in 1889, the production of biotite 
from chlorite has been affirmed by several writers of admitted 
authority. 
Professor Lossen, in the paper? on the crystalline schists com- 
municated by him to the International Geological Congress, which 
met in London in 1888,° distinctly takes my view. He states that 
biotite is produced in ‘“‘diabase” as the result of contact with granite 
and other eruptive masses, and he adds that this biotite is visibly 
formed at the expense of chlorite originating in “‘augite or primary 
hornblende.” 
-M. Michel Lévy, on the same occasion, communicated a paper * on 
an allied subject. He is describing the metamorphism of detrital 
rocks. In the first stage, the cement of the fragments forming (say) 
a sandstone is converted into chlorite and sericite. In a more 
advanced stage, “sericite and the chlorite give place to interlaced 
lamine of black mica.” 
A third writer, Prof. Salomon,° describes a case somewhat similar 
to the last, but the conditions are simpler. A phyllite is in contact 
with an eruptive mass of diorite, and the chief change produced in 
the phyllite is the conversion of chlorite into biotite. 
This mineral transformation has also been described by 
Ritidermann.*® 
I have not given the precise details of the causes of change in each 
of these cases, because my object is merely to record confirmations of 
1 On the Production of Secondary Minerals at Shear-zones in the Crystalline 
Rocks of the Malvern Hills, Q.J.G.S., August, 1889, p. 478. 
2 Winige fragen ziir Jésung des Problems der Krystallinischen Shiefer, nebst 
beitragen zu deren beautwortung aus dem Palaozoicum ; Compte Rendu, p. 180. 
8 This date is of course prior to 1889, but Prof. Lossen’s paper was not known to 
me till after mine had been sent in. 
4 Sur l’ Origine des Terrains Cristallins Primitifs; Compte Rendu, p. 58. 
5 Zeits. d. deutsch. geol. Ges. 1890, xlil. p. 450. 
6 Neues Jahrb. v. Beilage-Band (1887), p. 643. 
