146 



perhaps be correct to state that such phenomena, in some form or 

 other, are never absent from true glacial deposits. Amongst these 

 phenomena are the slickensided faces of drift, which were noticed 

 first, I believe, by the late Hugh Miller, and were termed by him 

 " striated pavements." These closely resemble the appearances 

 seen on the divisional planes of hard rocks near to a fault ; and 

 Hke these last, these "striated pavements" are due to the slipping, 

 in the plane of least resistance, of one part of a rock over another 

 part, under great pressure. In the case of fault-sUckensides, the 

 pressure that gave rise to these phenomena was apphed in what 

 was, practically, a horizontal direction, and the plane of striation, 

 following the plane of least resistance, is vertical (or practically so). 

 In the case of the glacial deposits, the stony paste was squeezed 

 against the hard rock by the pressure of the superincumbent mass 

 of ice acting from above downwards, and the plane of least resist- 

 ance lay, consequently, in a horizontal direction, and it is along 

 that direction, or that approximately, that the rock has slipped. 

 This is only another way of saying that the settling down of the ice 

 gave rise to small faults of very low hade, or as they might be called, 

 "thrust planes." These thrust planes very commonly severed small 

 deposits already laid down, and pushed one part (often with more 

 or less accompanying disturbance) many feet or many yards away 

 from the point where it originated. This phenomenon is well illus- 

 trated by the accompanying figures. 



Fig. 3. 



Disturbed Laminated Clays, probably originally deposited in nearly 

 horizontal sheets, and afterwards deranged by lateral movements resulting from 

 the down-settling of the melting ice sheet above. Length of section, 9 inches, 

 Midland Railway cutting near Langanby. 



