i8g 3 . SHELLY-SANDS AND GRAVELS. 433 



Straits" from the bight of Liverpool Bay, that many, if any, erratics 

 would cross it westwardly from Wales. 



Eskdale and Scotch granite are found along a base line from 

 Macclesfield to Carnarvonshire, and for the two granites to be so 

 distributed they must have crossed each other in their courses. The 

 much talked-of Riebeckite — which is identified with that of Ailsa 

 Craig, Professor Sollas informs me — has been found in the Drift 

 south of Dublin ; it also occurs west of Liverpool, as well as at 

 intermediate localities in Wales. For an Irish-Sea glacier to perform 

 this prodigy of distribution seems incredible. A glacier distributes 

 its load in stream-lines, and the stones from one side do not cross to 

 the other, and vice versa. 



5. — // the land has been submerged, deep-sea beds containing shells in the 

 position in which they have lived and died should be common, whereas there 

 are none. 



This is practically number 3 objection in another form — that is, the 

 fragmentary condition of the shells is considered to be a proof that a 

 glacier has passed over and crushed them. The difficulty of meeting 

 this objection is that we do not know what deep-sea beds under glacial 

 conditions would be like. There is a physical element that is entirely 

 overlooked, and that is the action of the tides. I have shown y that 

 the whole body of water is moved down to the greatest depths by the 

 tides, and not merely the surface. 



Most of the glacial beds that I have seen bear the marks of this dis- 

 turbance, in the form of current bedding, especially the sands. The 

 sands are intercalated in the clays, and it is difficult to separate the one 

 from the other. The Boulder Clays, according to my interpretation, bear 

 the marks of current action also in the smallness and rounded nature 

 of the shell fragments, the roundness of the grains of sand and their 

 high polish, and the manner in which sand-beds occur therein. The 

 proportion of sand to clay is generally very considerable, the small 

 gravel is also often highly polished and rounded. Numerous examina- 

 tions of low-level Boulder Clays by washing, sifting, and separation of 

 the grains, impresses me very strongly with the enormous wear which 

 every constituent particle of the Boulder Clay has undergone, some- 

 thing totally different to what is seen in sand washed out of a living 

 glacier which is uniformly angular. It is, therefore, quite probable 

 that such deep-sea beds as are asked for do not occur in tidal seas, or 

 if they do, only in exceptional positions. It is true the dredge brings 

 up live shells from the sea-bottom now, but it is a surface gleaning, 

 and the shell fragments are usually much more numerous than the 

 living examples. Molluscs dying on the bottom of a tidal sea would 

 not lie undisturbed, they would be rolled about with each tide, so that 

 it is quite possible that undisturbed beds may not be accumulated. 



8 Tidal action a geological cause. Proc. L'pool. Geol. Soc. Session 1S73-4 ; 

 also Phil. Mag., 18SS, vol. xxv.pp. 338-343. 



2 F 



