1 6 The Irish Naturalist. 



The change from the boulder clay to the contorted drift 

 marks some great change in physical conditions, the nature 

 of which we cannot at present fathom. The false bedding of 

 the lenticular masses of sand, the irregular disposition of the 

 gravel, often against buried cliffs made of its own material, 

 suggest frequently-changing currents, while the travelled 

 boulders, often bearing scratches, aiid the included marine 

 shells, seem to show that the currents were those of a sea still 

 laden with ice. 



The relations of the contorted drift to the boulder clay are 

 frequently of a remarkable character ; often narrow curving 

 cracks, filled with the sand and gravel of the drift, penetrate 

 the clay, isolating large lenticular masses of it two or three 

 feet or more in length. Sometimes genuine boulders of 

 boulder clay, many feet long and several feet thick, are to be 

 seen lying well within the midst of the contorted drift. But 

 most curious are the numerous pipes and irregular funnel-like 

 hollows, sometimes with vertical sides for a part of their 

 course, which extend downwards from the contorted drift into 

 the boulder clay. These are now filled with the sand and 

 gravel of the contorted drift, which in the upper part of the 

 hollow lies in downwardly converging stream-lines, while in 

 the lower part it is sometimes more or less horizontallystratified, 

 or lies in concave layers like a pile of watch-glasses. These filled- 

 up cavities are difficult to account for except on the supposition 

 that the boulder clay at one time included in its mass great 

 lumps of ice, and that as these melted away the overlying sands 

 and gravels poured down, displacing the water, and filling up 

 the resulting pit. That the melting and filling up were com- 

 pleted before the deposition of the gravelly boulder beds is 

 shown by the undisturbed manner in which these lie over the 

 down-streaming sand of the contorted drift. 



Much of the contortion of the last-named deposit is of 

 marvellous complexity. In a bed of sand not more than two 

 feet in thickness one may occasionally see in a length of a 

 dozen feet four or five folds, illustrating almost every type of 

 mountain structure, from the simplest anticlinal to the com- 

 pleted overfold with its reversed faults, or overthrusts ; and, 

 smoothing off every irregularity, there will follow upon this 

 another bed almost perfectly horizontal, and composed of 

 successive horizontal layers. 



