246 J. Clifton Ward — On Rock-fissuring . 



None of them are mucli more than from 12ft. to 20ft. in depth, and' 

 they are found not on the steep western sides of the mountain, but 

 for the most part on the stony table-land above the 2000 ft. contour. 

 They differ from the fissures of Helm Crag in being closed and 

 often grassy along their beds. In one case I found that a well- 

 marked and long trench joined up to the line of a small fault. 



Perhaps, however, the finest instance of this fissuring is that upon 

 the mountain-top just north-east of Illgill Head, overhanging Wast- 

 M'ater, a continuation of the line of craggy mountain forming the 

 Screes. The steep mountain-side above the lake presents no appear- 

 ance of slips, but OEf the summit the ground is cut up in the most 

 marvellous manner by fissures for the most part running in the same 

 direction as the hill-side. They are roughly parallel to one another, 

 and present a plan of what might be an area of faulted country, in 

 which the inequalities at the surface had been produced more quickly 

 than the denuding agents could remove or soften them down. In 

 one place may be seen a line of tumbled craggy rocks upon one side 

 of a line of fissure, the ground being depressed upon the other side ; 

 and in another place the apparent subsidence, or throw, has taken 

 place in an opposite direction ; while there is at least one good 

 example of a tract of ground let down between two parallel fissures, 

 reminding one of a trough fault. 



There are many other cases in the district of a similar nature to 

 the above, though not always so well marked, but in all those just 

 noticed there is no indication of a slipping away of the hill-side. 

 Instances where there is this indication are more frequent, but then 

 it is not the mountain-top that is fissured, but the mountain-side. 



The examples mentioned abov€, all occur in rocks of the Borrow- 

 dale Volcanic Series (Green Slates and Porphyries), nor have I yet 

 noticed any good cases of this class among the mountains made up 

 of the Skiddaw Slates. How are such fissures to be accounted for ? 

 Does any one of the following suppositions seem likely ? — 



1. That they are strictly of the nature of slips ; that is, the mass 

 of the mountain, or any part of its mass, is pressing outwards or 

 towards the flanks. 



2. That they have been caused by earthquake shocks, perhaps 

 very long since. 



3. That they are the outward expressions of faults slowly taking 

 place, and represent much greater disturbances or shifts at consider- 

 able depths. 



I can conceive of no other theories than these to account for their 

 formation. Let us consider their respective merits. With regard 

 to (1) the facts that the mountain-side has no slipped appearance, 

 and that the fissures often occur on a more or less flat-topped moun- 

 tain, are against this supposition, though the ease with which one 

 can imagine a great slip inclines one rather naturally towards it. 



That (2) is a possible cause no one will deny, though in this case 

 it seems almost strange that the fissures should not be more frequent 

 than they are, seeing that the shocks must always have been more 

 or less felt over so small a district whenever they occurred strongly 

 at one part. 



