Reviews—C. Reid & J. Groves—Purbeck Charas. 475 
thing lacking here being illustrations of a few leading fossils, just 
sufficient to help the student to recognize the chief fossiliferous 
strata as met with in the field. The last chapter, contributed by 
Dr. F. H. A. Marshall, embodies a most interesting and valuable 
summary of our knowledge of the geological history of the Domestic 
Animals. We only wish this chapter could have been more fully 
expanded. In conclusion, we congratulate Mr. Rastall on his 
admirable and luminous textbook, which should be in the possession 
of every teacher and serious student of agriculture. 
J. R. A.-D. 
TV.—Tue Purpeck Cuaras. 
T last. we are promised some definite information about the 
interesting series of Chara, so common in the Purbeck cherts. 
Hitherto the nature of the matrix has only permitted a study 
of sections of these plants allowing of imperfect examination. 
But the labours of Messrs. Clement Reid & James Groves resulted 
in the finding of Chara remains in a close-grained limestone, 
which permitted a fresh method of treatment. On treating pieces 
of limestone with a steady drip of slightly acidulated water the 
results were surprising even to the experimenters. The irregular 
mineralization of the limestone allowed the dripping water to rapidly 
attack the pure calcite and to leave the silicified matter standing in 
relief. As the Characee proved to be not pure calcite they were 
among the standing forms after treatment. And the authors have 
not only been able to obtain reliefs of fruits and stems, but even, in 
many cases, completely to remove fruits and stems from the matrix. 
The amount of new material is so great that there may be seven or 
even eight species of four genera. But they are so broken up and 
entangled that it will take much research to work them out properly. 
The most abundant form, however, is fairly well known, and 
‘Messrs. Reid & Groves have described it as Clavator, n.g., in Proc. 
Roy. Soc., B., vol. lxxxix, pp. 252-6, pl. viii, 1916; no trivial name 
is given, nor Is any type quoted, unless Messrs. Reid & Groves wish 
it to be understood that Saporta’s species (the only one mentioned) is 
to be so regarded. The editor is at fault in passing this omission. 
The paper is of remarkable interest and importance. 
V.—Tue Corretation or tHE Pre-Camprran Rocks or THE Recion 
oF THE Great Lakes. By A. C. Lawson. Bull. Dep. Geol. 
Univ. California, vol. x, No. 1, pp. 1-19. 
N this paper the author endeavours to draw up a correlation table 
for the pre-Cambrian rocks of Canada, based on the hypothesis that 
there have been in the region named two and only two great periods 
of granitic intrusion, each followed by its concomitant uplift and 
denudation, this constituting a major unconformity. The classification 
on this basis when reduced to its simplest terms is as follows: 
(1) Ontarian system, including the Coutchiching, Keewatin, and 
Grenville series. (2) Laurentian revolution, that is, the intrusion 
of the granite batholiths. (3) Epilaurentian interval, when the 
