Revieics—Prof. HuWs Phydcal Geology of Ireland. 173' 



breadth — to an ' enormous ' extent, ' thousands of feet ' in depth, 

 etc., so as to give the pressure which he thinks needful to have 

 originated this general outward motion in both opposite directions 

 from this axis. We should greatly have wished that he had given 

 us some idea of the actual physics of such a heap of snow, ' thou- 

 sands of feet ' in depth, perfectly unsupported on either side by any 

 more solid materials — or had shown the probability even of this 

 extreme accumulation which he supposes to have taken place over 

 this belt of country, ever amounting to such a differential excess as 

 to give him the required depth of ice.^ 



But is this idea of Mr. Close's so thoroughly established that we 

 are driven to the region of wild fancy to attempt an explanation of 

 it ? An immense mass of detail is referred to by Prof. Hull in 

 evidence of this supposed movement of the ice-sheet (pp. 236-259), 

 but all this evidence must be carefully analysed before we can 

 admit its conclusiveness. And the author must permit us to doubt, 

 and to doubt very seriously, if a great part of it is applicable to the 

 point at issue at all. He himself, and equally every other writer of 

 these glacial theories, insists on the necessity for 'experience,' and 

 a certain knowledge of the causes of these markings, scorings, 

 polishings, etc., appealed to as evidence of the movement, before the 

 observer can appreciate their force or value. And firstly it is urged 

 that in such matters we should take our lessons from the existing 

 centres of glacial action, such as the Alps, Norway, and Greenland. 

 How far has this been done ? How many of the dozens of observers, 

 whose notes have been culled, have studied these glacial phenomena 

 in their existing centres ? How many have been capable of dis- 

 tinguishing, or have attempted to distinguish, — or have even known 

 the necessity of such an attempt, — marks of local glaciation from 

 those due to the supposed general movement ? And if the whole 

 mass of evidence adduced be subjected to such a searching analysis, 

 how far will this idea of a linear axis of motion remain established ? 

 We confess we hesitate much before we can admit it. Our author 

 himself adds greatly to our feeling of the necessity for great caution 

 in such matters. In this way (at p. 115), speaking of " River 

 Terraces," the most recent of the "Drift" deposits, he says: — 



" Of these the most remarkahle and interesting from its historical and architec- 

 tural associations is the terrace at the lower end of Glendalough, at its confluence 

 with the vale of Glendasan, upon which stands the Eound Tower, and the Church of 

 St. Kevin. This terrace is composed of stratified gravel of rounded pebbles and 

 sand banked up against an old moraine which has been thrown across the valley. 

 The upper surface is level and it rises about twenty feet above the bed of the Glen- 

 ealo Eiver." 



Now if we turn to p. 197, we find that — 



" After careful examination I have also come to the conclusion that the Round 

 Tower and Churches of Glendalough are built on a moraine, which has been thrown 



1 Old Procopius held that on the tops of high mountains there never fell either 

 snow or rain, because they are above the highest clouds ! ! Bacon, in one of his 

 wonderfully sententious passages, says, " Adulterina res est in scientiis prascocem 

 esse et promptum, nisi etiam solidus sis et multipliciter insti-uctus." — Be Augm. 

 Sclent., lib. v. cap. v. 



