716 ME. J. E. MAER AWD DE. H. A. NICHOLSON 



the Ashgill Shales or Coniston Limestone on one side and by the 

 Browgill Beds on the other. The Ordovician and Silurian rocks 

 usually approach so near to each other that it may readily be seen 

 that there is no room for more than a small portion of the whole 

 thickness of the Skelgill Beds in the interval. The beds are there- 

 fore now preserved as a series of lenticular patches, the main portion 

 of the line of outcrop being occupied by little or none of them. 



(3) Smaller crushes of a similar nature can often be traced in a 

 single section, as, for instance, in the case already described of the 

 crushing-out of the shales of the argenteus-zone below the Upper 

 Bridge at Skelgill. 



(4) The hade of the fault may frequently be actually seen coincid- 

 ing with the dip of the beds ; and the line of fracture is often marked 

 by broken shale frequently farther crushed into a black mud. Where 

 the dip of the beds is different on the two sides of the fault, this is 

 probably a local phenomenon produced by the rucking up of the lower 

 beds during the process of sliding. 



(5) The occurrence of a quartz-vein along the line of movement 

 just below the promontory near the "Upper Bridge at Skelgill, which 

 coincides with the dip of the beds there, and the upper surface of 

 which is completely polished by the shales which rest on it, shows 

 that these shales have been moved over the nearly horizontal vein at 

 this point. 



(6) At the Lower Bridge at Skelgill it can be shown that some 

 15 feet more rock has been removed by the fault in the great cliff just 

 above the bridge than in the section just below it. Between these 

 two sections is the small dip-fault already described, which has a 

 downthrow to the E.jST.E. on the S.S.W. side of the stream, and one 

 to the W.S.W. on the ]Sr.:N'.E. side. This looks as if the tearing 

 away of the additional 15 feet of rock had been limited by a pre- 

 existing joint-plane, and that on this side of the joint the lower and 

 upper rocks had moved towards each other to fill up the gap so 

 produced. 



(7) It is probably due to the same process of stretching that the 

 great dip-faults, which frequently cause a lateral shift of the Coniston 

 Limestone to an extent of over half a mile, rapidly die out to the 

 south, so that beds some two miles south of the Coniston-Limestone 

 outcrop are scarcely affected. 



It has been stated above that the beds of the Stockdale-Shale 

 series undergo little alteration in character and thickness'' when 

 traced laterally. This is well shown by the remarkably exact 

 correspondence between the shales of the zone of Monograptus 

 argenteus, as seen in Skelgill and lEealy Gill. There is, however, a 

 certain amount of lateral change, as shown clearly by the great 

 thickening of the Browgill Beds between Stockdale Beck and 

 Spengill. The variations of thickness, so far as we have been able 

 to ascertain them by measurement, are indicated in the following 

 table : — 



