Anon s Dr. A. Holmes and Dr. 8S. Smith— 
normative. The normative compositions of plagioclase, pyroxenes, 
and opaque ore corresponds closely with those revealed by micro- 
scopic examination. 
The analysis as a whole is that of a typical oversaturated dolerite, 
_ and for comparison and contrast it is repeated below, together with 
analyses of the Whin Sill, of a dyke and lava-flow occurring in Mull, 
and of the Cleveland dyke. 
A B C D. E F 
SiO. 50-30 51-22 50°71 51-63 50°54 57-57 
Al,Os 14-1] 14-06 14:78 11:77 12:86 14-25 
Fe,0z 3°16 4:32 3°52 3-23 4:13 6-04 
FeO 9-90 9-03 8-95 10°52 $-75 3-95 
MgO 5:56 4-42 5:90 5-02 4:63 4:24 
CaO 8-54 8:33 8-21 9:34 8-74 6:87 
Na,O 2-34 2-55 2-76 2-90 2-42 2-98 
K,O 0-74 1-25 1:39 0-91 1:43 1-08 
H,0 + 1-94 i‘ ae NO 2:24 |) 
EO 2 1-01 \ We Ee \ioces ip ip 2 
CO, 0-16 0-19 0-25 0-11 0-19 0:30 
TiOg 222 2°42 1:92 2-00 * 2-80 trace 
P.O; 0-30 0:25 n.d. 0:29 0:26 0-15 
MuO 0-12 0-16 0:31 0:35 0-32 0:27 
BaO 0:03 n.d. n.d. 0:03 n.f. n.d. 
S Mets 0-26 n.d. 0:04. n.f 0:19 
Totals 100-43 99:74 | 100-48 | 100-28 | 100-12 99:14 
Sp. Gr. 2-98 2-98 )e a2 O4. a= a 2°77 
A.—Wackerfield Dyke. H. I’. Harwood, analyst. | 
B.—Whin Sill. Cauldron Snout, Durham. J. J. H. Teall, analyst. Q.JS.GS.,. | 
x], 1884, p. 654. 
C.—Whin Sill. Crags near Borcovicus, Northumberland. J. J. H. Teall, 
analyst. British Petrography, 1888, p. 209. 
D.-—Tholeiite of Brunton Type. Dyke near Kintallen Mull. E. G. Radley, 
analyst. Summ. Prog. Geol. Surv. for 1914, 1914, p. 55 (Lab. No. 411). 
E.—Basaltic lava, Mull. E. G. Radley, analyst. Summ. Prog. Geol. Surv. for 
1915, 1916, p. 26 (Lab. No. 448). 
*,—Cleveland Dyke, Great Ayton, Yorkshire. W. F. K. Stock, analyst. 
British Petrography, 1888, p. 206. 
It will be seen at once from inspection of the first three columns 
that the composition of the Wackerfield dyke (except in regard to 
potash) corresponds as closely with that of the Whin Sill as one 
analysed sample of the Whin Sill does with the other. Chemical 
evidence, therefore, strongly supports the view of type-identity 
already recognized by Miss Heslop, and developed here in the 
preceding paragraphs. The difference in potash is in accordance 
with the only noteworthy petrographical difference between the 
Wackerfield dyke and the Whin Sill, namely, the absence of 
recognizable micropegmatite and biotite from the former. The 
Hett dyke is petrographically identical with the Wackerfield dyke, 
but the old analyses which at present are alone available are 
