TJw Lieoloiju of Cuiinaidai 195 



but in general uniformity of stratification is well maintained. 

 The presence of erratics shows that the glacial conditions had not 

 passed away, and that icebergs occasionally dropi:)ed their included 

 material into the beds as they floated over. The general freedom 

 of the beds from foreign matter, however, shows that either the 

 icebergs were not very numerous or that they were but ill-supplied 

 with included rocks and boulders. There is no evidence to show 

 from what source the material composing the sandstones was 

 derived ; any erratics they contain are similar in character to tiie 

 boulders found elsewhere in the glacial beds. 



The beds we have classed as conglomerates bear a general 

 resemblance to the till or boulder clay of the glacial series of 

 America and Europe ; and may represent the ground-moraine 

 of the ice-sheet. The rude stratification they possess is very 

 similar to that seen in certain of the glacial beds of America and 

 Europe, but whilst the question of the origin of boulder clay 

 or till is so contested a point among the glaciologists of Europe 

 and America, we do not propose to enter into any detailed 

 consideration of it. To each of the writers of the paper the 

 appearance presented by the till of Great JJritain is well known, 

 and w-e are satisfied by oljserving that between the "till" .and the 

 beds classed by us as conglomei-ates, there is a strong general 

 resemblance. 



With regard to the foimation of unstratified mudstones it may 

 be pointed out that when a sub-glacial stream entered a lake 

 where the separation of the ice from the bottom was very 

 imperfect, the chanjiel along which it flowed might .speedily 

 become gorged with sediment, forcing the stream to carve a new 

 patli through the ice. If the supply of sediment v/as great this 

 might lead to the formation of beds showing little or no stratifica- 

 tion ; but when the stream reached that position under the 

 ice-front which would allow of the more gradual distribution of the 

 sediment it carried stratification would begin to show. There 

 would tiius be a lateral passage or transition from unstratified 

 to stratified beds — a feature often met with in the glacial series. 

 There might also be a gradual transition from the true ground- 

 moraine of the glacier into the sub-aqueous beds. Possibly 

 the constriction of the channel occupied by the glacial stream 

 may afford a clue to the explanation of the patches of water-worn 



