. 688. 
Vol. LVIII of Whole 
Series. 
The 
eologica 
OR 
Montbly Journal of Geology. 
WITH WHICH IS INCORPORATED 
Eats CEO E@O GIST. 
Founded in 1864, by the late DR. HENRY WoopwarbD, F.R.S. 
EDITOR ee 
H. RASTALE Se b:, 
M.Inst.M.M. - 
ASSISTED BY 
Pror. J. W. GREGORY, -D.&c., F.R.S. 
Ff, H. HATCH, Pu.D., M.Inst.M.M. 
PROF. J. HE. MARR, Sc.D., F.R.S. 
A. SMITH WOODWARD, LL.D., PR.Seem 
sin JETHRO J. H. VEHEALL, Sc.D., F.R.S. 
PROF. W. W. WATS, Sc.D., F.R.S. 
HENRY WOODS, M. AL polar. 
Vath in Stity, ~ 
i 
aR 
OCTOBER, 1921, 
921 
ace 
CONTENTS :— 
Page 
EDITORIAL NOTES 
ORIGINAL ARTICLES. 
Percentages of Igneous 
By V. A. HYLES and 
(With 8 Figs.) 436 
By Dr. A. 
Silica 
Rocks. 
J. B. SIMPSON. 
The Wackerfield Dyke. 
HOLMES and Dr. 8S. SMITH. 
(With Plate VIII and 3 Figs.) ... 440 
The Foraminifera of the Hartwell 
Clay. By HH. IWNEAVERSON. 
(With Plate EXC) ints: cont clean 454 
LONDON: DULAU 
Ne 
ational Mus wy 
ie ee 
ORIGINAL ARTICLES (continued). Page 
An Alteration of Shale at Wensley, 
Derbyshire. ByC.S. GARNETT. 473 
REVIEWS. 
The Geology of Pembroke and 
MIMors parecer ssschestics ie tasertoseerins 479 
Field Mapping for the Oil Geologist. 480 
REPORTS AND PROCEEDINGS. 
IBrihishwASsoclatlolnmeccastseree ees 480 
& ©O., Lrp., 34-86 Marcarer STREET, 
CAVENDISH SQuaRE, W.1. 
