Review of decent Geological Literature. 1 2 1 
bj melting, settled to the bottom to be covered up bv layers of fine claj. 
Torrents from melting glaciers, coming down from the land areas to the 
north, were the bearers of the material composing the stratified clay. 
Usually the sand-boulders lie horizontally, but occasionally they are 
found thrown upon their edges. Sometimes the^' show signs of having 
been jammed and broken as if in an ice-pack. 
The facts are significant and reveal a state of things that we have 
every reason to believe was repeated whenever there were bodies of 
water contiguous to the southern limits of the great glacier. 
On the orgajjic origin of the chert in the Carboniferous limestone series o/ 
Ireland and its similarity to that in the corresponding strata in North Wales 
and Yorkshire. By Dr. George J. Hixde. (Geological Magazine, De- 
cade III, vol. iv, October, 1887). This paper was read before the British 
Association at its Manchester meeting last summer. It is a continua- 
tion of the discussion relating to the Carboniferous chert, begun bv 
Messrs. Hull and Hardman, in a joint paper published in the scientific 
transactions of the Royal Dublin Society, 1878. 
Messrs. Hull and Hardman, after chemical and microscopic examina- 
tion of the chert from the Carboniferous rocks of Ireland, reached the 
conclusion that the chert was of inorganic origin, that the silica, held in 
solution in percolating water, replaced portions of the limestone by a 
process of pseudomorphism, and that there was absolutely no evidence 
that the chert originated directly or indirectly in such organic products 
as sponge spicules, diatoms or polycistines. 
Prof. Sollas in 18S1 re-examined some of the microscopic sections pre- 
pared by Prof, Hull in the course of his investigation, and pronounced 
certain rod-like or tube-like structures that Prof. Hull seems to have 
taken for minute crinoid stems, to be nothing but spicules of sponges. 
Dr. Hinde visited numerous localities in Ireland for the purpose of exam- 
ining and collecting Carboniferous chert. Among others the typical 
localities from which Prof. Hull's material had been derived, were ex- 
amined and specimens seciu'ed. Microscopic sections were prep.'ired 
from specimens from every locality visited, with the result that sponge 
spicules were more or less conspicuous in every section. Ordinarily the 
rock is crowded full of spicules. Fragments of brachiopod and entomos- 
tracan shells and a few crinoid plates were detected, but no foraminifera. 
Respecting the chert from the Carboniferous strata of North Wales 
and Yorkshire Dr. Ilinde points out that in all essential features, litho- 
logically and chemically, it is identical with the Irish Carboniferous 
chert, and then adds: "The organic nature of the English and Welsh 
Carboniferous chert, as produced from sponge-remains, is far more 
distinctly shown than in the case of the Irish beds, for the spicules are 
much better preserved, and the beds have been less altered bv fossii- 
ization." 
The profusion of sponges during the later Carboniferous, in the area 
now occupieii by Great Britain and Ireland may be inferred in the 
statement that "In some of the Yorkshire areas there are beds of chert 
