688 EEroRT— 1887. 



of quartz in t.lie felspar is a thing whicli is specially common to the granitoid rocks 

 of the Hebridean series of Britain and the Laurentian of America. But of course 

 I cannot assert it is Hehridean, only it reminds me of Hebridean.' 



The presence of these foreign boulders in coal seams opens out several interest- 

 ing inquiries. The two main questions are — Whence did they come ? and by what 

 means were they brought into their present position ? 



Many suggestions liave been hazarded and tlieories broached to answer these 

 questions, but none as yet fidly accounts for all the phenomena connected with 

 these boulders. We have seen that they are not confined to our own little island, 

 but are found under exactly similar conditions in North America ; so, whatever the 

 agent of transport was, whether water or ice, it was evidently active over a large 

 part of the northern hemisphere. 



The similarity and almost identity of the mineralogical composition of these 

 boulders is very remarkable, coming as they do from areas so widely separated as 

 are our own shores from those of America. 



They are evidently older than any rocks of the Carboniferous period, but whether 

 they are fragments of some ancient continent of Cambrian or Archaean age has yet 

 to be decided. 



As to the mode of deposition of these boulders in the seams of coal, many objec- 

 tions surround the theory of transport by currents of water, seeing the great size 

 of some of these blocks and the total absence of any associated clays or sands. 



Transport by ice, floating icebergs in a summer sea, would, perhaps, explain 

 better than any other theory their position, and often isolation, in strata singularly 

 free from extraneous matter. 



Professor CroU, in his ' Climate and Time,' suggests that the Carboniferous flora 

 was the growth of one of those assumed interglacial stages, recurrent during all 

 geological time, and that during the intervening cold periods represented, I pre- 

 sume, by the grits and sandstones, we had the most favourable conditions for en- 

 tombing and preserving the vegetable life of that epoch. 



But an objection to this theory is, there is nothing in the character of the vege- 

 tation during the whole of the long period embraced by the Coal-measures to sup- 

 port the argument. The flora is identical and indicates no change of climate during 

 the millenniums of millenniums represented by the thousands of feet of thickness 

 of the Coal-measure rocks. 



Such are some of the unsolved problems represented by these boulders, and 

 nothing but a careful accumulation of facts with regard to them will help to un- 

 ravel their mvsterious historv. 



4. On the Organic Origin of the Chert in the Cailioniferuus Limestone Series 

 of Ireland and its Similarity to that in the Corresponding Strata in 

 North Wales and Yorkshire.^ Bij Geokge Jennings Hinde, Ph.I). 



The origin of the chert in the upper division of the carboniferous limestone 

 in Ireland was the subject of a joint paper by Messrs. Hull and Hardman" in 

 1878, in which they stated that the silica of which it is composed was derived 

 directly from the sea-water ; that the chert was essentially a pseudomorphic rock 

 consisting of gelatinous silica replacing limestone of organic origin ; and 

 that it was not due to the action of organisms with siliceous skeletons, such as 

 diatomacete, polycystinse, and the spicules of sponges. In the same year M. A. 

 Henard attributed a similar origin to the phthanites of the Carboniferous series of 



' The orio'inal paper has been published 'm cxtcnso in the Gcol. 3Iag. for October 

 1887, N.S. Dec. 3, vol. iv. pp. 435-44G. 



- On the Nature and Origin of the Bods of Chert in the Upper Carboniferous 

 Limestone of Ireland. By Professor Edward Hull, M.A., F.R.S., Director of the 

 Geological Survey of Ireland. 



On the Chemical Composition of Chert and the Chemistry of the Process by 

 which it is formed; By Edward F. Hardman, F.C.S. — ScienUJio Transactions Hoy at 

 DuUin Society, vol. i. N.S. 1878, pp. 71-94, pi. iii. 



