Dr. C. Callaway—Rock-Metamorphism. — 537 
It is evident that we cannot trace potash under the microscope. 
Some of this alkali is furnished by the decomposition of the felspar 
of the diorite. An analysis of the medium-black diorite (my No. 1), 
made by Mr. Player, gives a percentage of 2°8 of potash. Another 
percentage by the same analyst is 3:9. In this case the diorite is 
the same variety as the first, but it has been slightly modified, and 
contains a little biotite. An analysis by Mr. Player of the coarse- 
grey diorite! (No. 8) yields 4:3 of potash; but this percentage is 
probably exceptionally high, as another of his analyses of the same 
rock, slightly crushed and decomposed, gives only 25 per cent. of 
potash. The schist formed out of this diorite contains 3:7 per cent. 
of this alkali, but in a schistose rock which is just graduating into 
this schist the percentage of potash is as low as 1:9. It appears 
then that at Malvern diorite itself supplies a certain amount of potash 
for the construction of biotite. 
Another source of potash is the adjacent granite? The effect of 
the infiltration of potash is seen in the production of biotite in diorite 
in the proximity of the veins. Analyses were made by Mr. Player 
of rocks in the section? at the southern end of Swinyard’s Hill. At 
a few yards from the veined complex the diorite (No. 1) contains 
only 2:8 per cent. of potash. In contact with the complex of veins, 
the diorite is changed into biotite-gneiss, where the proportion of 
potash has risen to 5-3 per cent. There seems then to be little 
difficulty in accounting for the potash necessary for the conversion 
of chlorite into biotite. 
We have next to consider the loss of magnesia and water. The 
reduction of the percentage of magnesia in the transformation of 
diorite into sericite-gneiss or into biotite-gneiss is demonstrated by 
analysis. Four analyses (Mr. Player’s) illustrate the change from 
diorite to sericite-gneiss. The magnesia percentages are respectively 
5:0, 5°3, 4:1, 2°6. The first (5-0) is from the uncrushed diorite ; 
the second (5:3) is from the diorite crushed and decomposed; the 
third (4:1) is the rock crushed into a micaceo-chloritic grit; the 
fourth (2:6) is the sericite-gneiss. Two analyses of the same schist 
made at Owens College under the direction of Dr. Cohen give 
respectively 1:29 and 0:35 of magnesia. Analyses made by Mr. 
Player of rocks from the Swinyard’s Hill section illustrate the 
change into biotite-gneiss. They give 7:3 of magnesia in the 
ordinary diorite, and 1:9 in the resulting biotite-gneiss. Another 
specimen of the latter yields to an analysis by Mr. Waller 2:8 of 
magnesia, and this rock passes into varieties in which two analyses 
give respectively 1-9 and 1:4 of magnesia. The elimination of 
magnesia is therefore clearly shown. 
Water was not separately estimated in the analyses made for me. 
Its elimination would seem, however, to offer no serious difficulty. 
1 This rock contains too much potash for a normal diorite. As a large proportion 
of the felspar is plagioclase, and the silica percentage is only 47, it can hardly be a 
syenite. 
2 Discussed in Quart. Journ. Geol, Soc. (1889), pp. 482-487, 499. 
3 Ibid. p. 482. 
