Present Aspects of Glacial Geology. 547 



present. The water percolating through this calcareous deposil 

 would no doubt soon get charged with lime, so that the acids would 

 be neutralized and incapable of acting upon the shells. Be this 

 as it may, I observed in many places delicate shells in all stages 

 of decomposition, and so friable that under ordinary subsoil con- 

 ditions I have no doubt they would have long ago disappeared in 

 solution and left no trace behind. In the deposits at Gloppa and 

 Tryfaen the shells and shell fragments are of a much stronger type, 

 and appear to have become in many cases partially hardened and 

 fossilized, as, indeed, is often the case with our Low-level Boulder- 

 clay shells. On Tryfaen also there formerly existed a protective 

 covering of Boulder-clay lying on the sands and gravels. 



The subject I have ventured to deal with in this address is a very 

 wide one ; it has been studied by many minds in many countries, 

 and after fifty years of work perhaps there is less theoretical agree- 

 ment now than there was in the beginning, although I think I see 

 signs that a development of the older ideas is gaining ground. 1 

 I venture to think that the questions that have arisen, and which 

 will arise in the future, are essentially of a character in which 

 inductive methods are required for their solution. Whichever view 

 is taken, whatever theory propounded, there are many facts known 

 to working geologists which do not range themselves under any 

 one hypothesis. Of late years thei-e has been a tendency to aim at 

 almost mathematical pi'ecision in the explanation of laws which are 

 supposed to govern these Ice- Age phenomena. To my mind, the 

 facts which I have been collecting for the last quarter of 'a century, 

 having seen the whole of the leading examples of High-level Shelly 

 Drifts in Great Britain and Ireland, as well as made a detailed study 

 of the most prominent of them, together with the Low-level Shelly 

 Boulder-clays and Sands over large areas, as also the essentially 

 glacial and land-ice phenomena of the Welsh and Cumbrian 

 Mountains, lead me to think that the precise, deductive, and 

 dogmatic method so much in vogue is ill adapted to evolve truth 

 from these varied and often, apparently, contradictory facts. For 

 my own part I feel that I have gained by my observation and 

 studies a certain little space of sure ground on which to place my 

 lever, but I confess with sorrow that there are many points on 

 which my judgment is less sure than it was in the first few years 

 of study. 



Let us first deal with what appears to be the axiom of a certain 

 class of glacialists, for it is interesting to observe that even those 

 who favour the land-ice as opposed to subaqueous theories differ 

 considerably among themselves. This axiom is, that all the shells 

 and shell fragments found in either the Low-level or High-level 

 Drifts are " boulders," that is, they have been removed from their 

 original habitat and carried to the places where they are found, 

 whether at high or low levels, whether on the coast or far inland; 

 furthermore, the carrying agent or pushing agent, as the case may 



1 Professor Bonney has lately given an excellent resume of the whole subject iu 

 his interesting book, " Ice-Work, Present and Past." 



