372 Reviews—Kendall’s British Iron-ores. 
Meanwhile our author belongs to the second type. He describes 
all the previously known species of Pholadomya, ranging from the 
Lower Lias to the Kimmeridge, under 19 names, which include no 
less than 60 of those recognized by his predecessors, and of these 
P. decorata runs from the Lower Lias to the Inferior Oolite, 
P. Murchisoni from the Bajocian to the Callovian, and several others 
have nearly as wide a range; even these are said to show passages 
into each other, and the last named is said to be certainly the origin 
of P. exaltata. It is very probable that these two types of paleon- 
tologists represent two phases in the evolution of the geological know- 
ledge of a country. In the earlier stages, when only an outline of 
the geology is known and the workers are few, it may be necessary 
to take a more general view; but as the details of the stratigraphy 
become familiar it is possible to come to closer quarters with the 
question of the succession of forms, and it is certain that the solution 
of this question can never be obtained without the most minute 
discrimination of varieties, while a correct one is impossible if in the 
midst of these details we lose sight of the wider laws. 
As a sort of appendix we have descriptions of Arcomya and 
Goniomeris, a new genus, and it is a curious thing that all the 
species in these two genera are described as new. ‘This part was 
written later. If species are taken in as wide a sense here, as the 
author does in the genus Pholadomya, one fancies one could match 
some of these amongst old Corallian friends. Has the author’s 
idea of species become more limited in the interval ? J. F. B. 
VI.—Tue Iron-ornzs or Great Brirain anp IRELAND, their Mode 
of Occurrence, Age, and Origin, and the Methods of Searching 
for and Working them (with a notice of some of the Iron-ores 
of Spain). By J. D. Kenpatt, F.G.8. 8vo. pp. xvi. and 480, 
with Illustrations. (London: Crosby, Lockwood & Son, 1893.) 
RON may justly claim to be one of the most important of all the 
elementary substances, not only by reason of its vast economic 
value to mankind, but also from its distribution in rocks of all ages 
which build up the framework of our globe and it is probably 
equally widely distributed throughout the universe. 
Its presence in the stratified deposits is indicated by their colour- 
ing, which is no doubt largely owing to this metal. Rusty-brown tints 
are due to hydrated peroxide of iron; brighter red tints, and some- 
times darker stains, are due to anhydrous peroxide of iron; greenish 
colours are produced by the protosilicate, and bluish tints are 
imparted by bi-sulphide of iron. 
Notwithstanding the immense abundance of iron in the earth’s 
erust, metallic iron, in a more or less pure condition, is but rarely 
met with. Indeed, until of late years, it was believed that all, 
or nearly all, such metallic iron was of extra-telluric, or meteoric 
origin, with the exception of ferruginous metallic platinum. True 
meteoric iron usually, if not invariably, contains nickel, to the 
extent: of 1 or 2 parts per 100 of iron, up to considerably larger 
amounts; the Fallas Meteorite, Siberia, containing nearly 11 per 
