Dec. 21, 1883.] 



♦ KNOWLEDGE ♦ 



373 



through a few miles of natural tunnelling in the marble 

 mountains of Carrara. 



" In limestone districts small rivers are in the habit of 

 suddenly disappearing, and breaking out in fresh places a 

 few miles distant. A legion of legends are based upon 

 these, that of Alpheus and Arethuea being the most 

 popular and typical. When I visited the fountain of 

 Arethusa it was the public laundry of Syracuse, and not 

 one nymph, but above a score of nymphs were there. It is 

 a considerable stream, that breaks out through a limestone 

 tunnel directly on the sands of the seashore. 



" There are about half-a- dozen of such subterranean 

 streams in the Craven district of Yorkshire, and more than 

 a dozen in Ireland. 



" The solvent power of the water reaches its maximum 

 when it has oozed through a peat bog. The river con- 

 necting Lough Mask with Lough Conn is a striking 

 example of this. Its subterranean evolutions are most 

 complex, and the hard limestone is riddled with caverns of 

 all sizes, from little holes aflbrding winter quarters for 

 solitary toads to the show caverns that are duly exhibited 

 to tourists for a consideration. 



" An absurd result followed from this condition of the 

 rock. A canal for extending the inland navigation from 

 Lough Corrib to Lough Mask, thence to Lough Conn and 

 the |Moy River to Killala Bay was projected, thus con- 

 necting Galway Bay with the Bay of Donegal. The canal 

 was actually cut in the hard rock between the lakes, and 

 finished all ready for filling. When the water was ad- 

 mitted it disappeared, and the cutting now remains as a 

 costly tributary to a subterranean river." 



EVIDENCES OF THE GLACIAL 

 PERIOD. 



IT is hoped that this paper may be useful alike to tliose 

 who have no accjuaintance with geology and to those 

 who have some knowledge of that science. To the former, 

 its chief object will be to enumerate in a brief summary — 

 " plainly worded, exactly described " — the evidences which 

 have led geologists to the belief in a Glacial Period ; while 

 to the latter it may not be altogether useless as a con- 

 venient summary of such evidences. The writer, therefore, 

 begs the indulgence of his readers if in some cases he has 

 been somewhat elementary and given to rejietition, for 

 which his only apology must be the desire to make the 

 truths of science plain and clear to all. 



When we see the ruins of a house with charred timbers 

 and blackened walls, we conclude at once that that house 

 has been burnt by fire. It does not matter if we have not 

 seen the fire ourselves, or if no one has told us about it ; 

 we still feel certain that fire has been at work, simply 

 because we know from experience that it is in the nature 

 of fire to char timbers and blacken walls, and because wc 

 know of no other cause capable of producing those results. 



It is by a precisely similar train of reasoning to the 

 ab(i\e that we feel certain that glaciers or rivers of ice 

 oni'(! ploughed their way down our English valh'ys, and 

 that a covering of solid ice onc(> enveloped the whole of 

 England. We believe this because throughout England 

 are marks upon the scenery of the country which glaciers 

 and ice are elsewhere jiroducing to-diiy, and which we 

 know of no other cause capable of producing in England 

 during the past, except that of the same agents of glaciers 

 and ice ; therefore, we conclude that these agents did 

 formerly exist in England, and we give to the time when 

 such was the case the name of the Glacial Period, 



In order that our readers may be able to verify this con 

 elusion for themselves we shall now describe a few of thote 

 marks in the scenery to which we have referred as being 

 produced by glaciers. 



(1.) Moraines. — In Switzerland, where glaciers exist at 

 the present day, wherever those glaciers occupy the valleys, 

 moraines are found. These moraines are composed of frag- 

 ments of rock, large and small, which, having become 

 detached from the adjoining hillsides, roll down on the 

 glacier, and are carried along by it, forming long continuous 

 lines of blocks and fragments along its sides. When this 

 accumulation is found along the sides of glaciers it is 

 termed a lateral moraine ; when, owing to the junction of 

 two glaciers from separate valleys, two of these side or 

 lateral moraines unite to form a central line of blocks and 

 fragments, the latter is called a medial XDoriime ; and when 

 a glacier comes to an end through having descended into 

 regions too warm for its existence, and where it is melted 

 away, a vast heap of rubbish brought down by the glacier 

 is thrown down at its termination, which is called a 

 terminal moraine. Now, exactly similar lines and heaps 

 of blocks and fragments are found in our English valleys, 

 and as we know of no cause capable of producing them 

 except glaciers, it is only reasonable to suppose that those 

 found in England are diie to the same causes as in Switzer- 

 land, and therefore we come to the conclusion that, although 

 glaciers do not now exist in England, they did formerly, 

 and then produced those moraine lines and heaps which we 

 now find in our valleys. 



(2.) Polished and Striated Rock Surfaces. — When a 

 glacier passes over a rocky surface, it polishes and makes 

 the same quite smooth and bright. Sometimes it makes 

 scratched markings upon such surface. This is done by 

 pieces of hard and sharp rock which have got frozen into the 

 glacier, and such markings are generally pretty near parallel 

 and in the same direction, consequently showing thedirection 

 in which the glacier is moving. Now very many of these 

 polished and scratched rock surfaces are founded in 

 England, and as they present an identical appearance with 

 those found in Switzerland, it is but reasonable to set down 

 both to the same cause — namely, glaciers. 



(3.) Erratic Blocks. — At many jilaces in Yorkshire may 

 be seen large boulders of granite, mountain limestone, <fcc., 

 several tons in weight, some being of exactly the game 

 material as that composing the mountains of Cumberland. 

 In fact several boulders of granite to be seen lying on the 

 clifi's of Yorkshire have evidently been derived from Shap 

 Fell in Cumberland. Now the question arises, how have 

 these very heavy boulders been brought down from Cum- 

 berland to Yorkshire 1 For a long time this question was 

 a perfect puzzle, until it was observed in Switzerland that 

 large boulders had been carried down from the Alps by 

 glaciers and spread over the plains below, in some cases 

 extending as far as the foot of the Jura mountains. Here, 

 then, was the clue to the mystery. A power had been dis- 

 covered capable of removing immense and heavy blocks of 

 rock for long distances— that power was the glacier ; and 

 as no other power but moving ice was known capable of 

 removing these heavy blocks, it became evident that it 

 could only have been ice which had removed these huge 

 blocks of Shap Fell granite to their present place on the 

 Yorkshire plains and clitfs. From these " erratic blocks," 

 as they are called, licing dispersed all over England, and not 

 always in a line with the present valleys, it is concluded 

 that during the severer portions of the Glacial Period, 

 England not only had her valleys filled with glaciers, but 

 that the whole country was "moulded" in ice, from the 

 higher portions of which, such as these Cumberland moun- 

 tains, erratic blocks were dispersed in all directions. 



