236 MR. C. DAVISON ON THE 



course, a slow movement, almost imperceptibly slow, but, as it will 

 be seen, far from unimportant. 



Apart from the resistance to motion offered by vegetation and 

 earthy matter, the stability of scree-material depends largely on the 

 form and lie of the stones and the slope of the surface, these condi- 

 tions being themselves connected. If the stones be nearly cubical 

 in form, they will be found to lie at all angles, often with their 

 edges leaning on surfaces sloping in opposite directions. The sta- 

 bility is naturally great in such a case, unless the stones be small. 

 On the other hand, if the stones be flat-shaped, as in most slaty 

 screes, they rest with their flat surfaces on the edges and faces of 

 those below, inclining outwards and downwards at angles more or 

 less approaching that of the scree-talus. Large blocks are more stable 

 than small ones, not only on account of their greater weight, but 

 also because they are generally imbedded amongst a number of 

 smaller stones, and thus can hardly be regarded as surface-stones. 

 Still, it is far from unusual to meet with blocks five feet or more in 

 length lying quite on the surface of screes and in a position suit- 

 able to creeping. 



A good example of a case in which the conditions are favourable 

 to movement, and especially to creeping, occurs near the top of 

 Hindscarth, a mountain in Cumberland, 2385 feet in height. On 

 the west side of this mountain, not far below the cairn, are several 

 Bheets of loose fragments of well-cleaved slate. The sheets may be 

 a foot or more in depth, and are inclined at an angle of about 20°. 

 The pieces of slate are of all sizes up to a foot or a foot and a 

 half in length, and are generally very thin, the largest not being 

 Inore than about an inch in thickness, and even this amount is un- 

 usual. They lie with their flat surfaces on the bare hill-side or 

 resting on those of other stones, nearly all inclined at the same 

 angle as the slope. They are mostly long-shaped, and, with few 

 exceptions, both large and small stones lie with their lo^iger axes 

 pointing down the slope, showing that, during motion, they have 

 placed themselves in the position of least resistance. 



Such conditions are I suppose unusual ; but, as a general rule, 

 the majority of the stones on the screes with which I am acquainted 

 slope outwards and downwards, and are therefore in a position for 

 creeping. The eff'ects of creeping, moreover, are not confined to the 

 mere descent of the stones. The movement of a stone in this way 

 may withdraw its support from others resting on it. It may easily 

 be imagined also that the stones may be of such a form and so ar- 

 ranged that a very slight movement in one may cause both it and 

 some of those in contact with it to topple over ; and, once in motion, 

 they will drag many others along with them before they finally come 

 to rest. 



Again, the entire surface of screes is exposed to every change of 

 temperature, and, throughout their whole extent, every stone that is 

 free to move will make, with every change of temperature, a small 

 slip downwards. The importance of this wiU be best shown by an 

 example. 



