is 93 . SHELLY-SANDS AND GRAVELS. 435 



only two arguments to answer, namely, the occurrence of boulders at 

 a higher level than the parent rocks, and the supposed improbability 

 of a subsidence of the land to the extent required by the submergence 

 theory. The former I have shown is explicable by ordinary sea 

 action assisted by shore-ice, and the latter is no improbability but a 

 difficulty born of unfamiliarity with ordinary geological phenomena. 



It is now time to turn our attention to the difficulties presented 

 by the alternative hypothesis — that of the Irish-Sea glacier — and 

 here, indeed, we are at a loss where to begin, they are so many and 

 various. A huge machinery of ice-sheets is called in to explain the 

 carrying up of boulders above their origin, though no examples of the 

 power of ice-sheets to do this are given. The crushing of the shells 

 is referred to the same agent, though many examples are known of 

 glaciers passing over soft beds without disturbing them. At the same 

 time, delicate shells found on elevated lands far inland have to be 

 accounted for, and it is suggested that they have been safely conveyed 

 frozen in the ice-sole of the Irish-Sea glacier which carried them over 

 hill and dale to be washed out and deposited on the final melting of 

 the ice. The rounding of the gravel and boulders and their deposit 

 on the hill-tops, it is said, took place in a somewhat similar manner; 

 but, as usual, no existing examples of such action are referred to, nor 

 is it explained why the deposits on hill-tops should be more water- 

 worn than those on the plain. To account for the distribution of the 

 erratics, either several glacial and interglacial periods are required, of 

 which there is no record, or a most extraordinary set of currents of 

 ice and undercurrents are postulated ; everything, in fact, except vortex 

 movement. Yet, with all this complicated machinery, none have 

 been able, in theory, to satisfactorily get the stones on one side of the 

 Irish-Sea glacier carried to the other side. Finally, the physics of the 

 ice-sheet are not subjected to a quantitative test. 



When we call up before our mental vision the simple and well- 

 known facts of nature which suffice to explain the marine drifts on 

 the theory of submergence, it seems unnecessary to resort to the 

 ingenious and artificial system of physics elaborated to explain the 

 phenomena by land-ice. 



When we have more knowledge of the glaciers of the Arctic 

 Regions, and facts, in place of ingenious suppositions, to base our reason- 

 ing upon, we may possibly have to revise all our glacial conceptions. 

 In the meantime, the submergence theory of the origin of the high-level 

 shelly gravels and sands seems to me by far the simpler of the two 

 theories, and the most consistent with the facts and phenomena which 

 the labours of a succession of enthusiastic geologists have made us 



acquainted with. 



T. Mellard Reade. 



2 f 2 



