158 U. M. Deeley — Disturbed Gravels. 



suppose have never been covered by glacier ice, even when occurring 

 within the glaciated areas. When studying the deposits of the Trent 

 Basin 1 I was very much interested in these surface features. They 

 were never seen in the low-lying gravels ; but always very marked in 

 those resting with their upper surfaces 25 feet or more above the 

 alluvial plain. That they were due to the action of ice in some form 

 or other seemed the only possible explanation. At that time, and 

 indeed until I had seen some of the Thames gravels, the most likely 

 theory of their formation seemed to be the movement over them of 

 glacier ice for very short periods of time. This seemed to be 

 supported by the trend of the axes of the disturbances, which was 

 almost, if not always, such as to indicate a movement down the valleys. 



Another peculiar feature of these surface disturbances in the 

 Trent Basin deserves notice. In this area we have fluvio-glacial 

 gravels of two very different lithological characters. The one was 

 formed by ice which came from the west, and is destitute of flints 

 where undisturbed. The other contains flints throughout, having an 

 easterly origin. For the flints to penetrate several feet deep into 

 the flintless deposit was a great difficulty, and seemed to require the 

 operation of a force acting from without. 



If ice in glacier form be out of the question on the south side of 

 the Thames Valley, another explanation must be looked for. The 

 explanation about to be proposed requires further field work before 

 it can be accepted as correct ; for it is necessary that what is now 

 going on in veiy cold climates should be more carefully studied. 



Fig. 4, p. 471, in my paper on the Pleistocene Deposits of the 

 Trent Basin, 2 shows a typical form of the phenomenon. Here we 

 have rising up towards the surface waves composed of very complex 

 masses of sand and gravel. Between these waves lie deposits of more 

 sandy material containing pebbly festoons and streaks. At their 

 bases the "waves" consist of the disturbed gravel and sand beds 

 below ; but as we rise the deposit becomes less and less stratified and 

 finally loses all signs of stratification. The material between the 

 waves of gravel is quite sandy and shows traces of very irregular 

 bedding. It is remarkably like a rainwash we should expect to be 

 derived from the gravel, and it retains this character even when the 

 pockets penetrate as much as six feet into the hollows between the 

 waves. But how can we account for rainwash in such a position ? 

 The sides of the gravel waves are too steep for them to have existed 

 Avithout the rainwash in their troughs. 



The phenomena we are dealing with may have been formed in the 

 following manner during periods of intense cold. During the summer 

 the whole mass thaws, and the water-level in the gravel lies five or 

 six feet below the surface. In the winter the frost penetrates the 

 gravel, but does not disturb it until the water-level is reached. As 

 the water freezes the ice expands sideways as well as vertically. 

 But it is not free to expand horizontally everywhere. Imagine that 

 it expands over definite areas and that crushing takes place on the 



1 "The Pleistocene Deposits of the Trent Basin": Q.J.G.S., 1886 r 

 pp. 437-79. 



2 Q.J.G.S., 1886. 



