GEOLOGY. 1 1 



sedimentary rocks, and in Teesdale and Tynedale it would 

 seem to be nearly or quite uniform in its geological position, 

 which is always below, but not far below, the Tyne bottom 

 limestone which forms the uppermost band of the series of beds 

 which has just been noticed. Generally it is fine in grain and 

 dark in colour, and forms rudely prismatic vertical columns. 

 At the Caldron Snout, where the foaming waters of the Tees 

 leap down a basaltic ravine two hundred feet in depth, this 

 columnar structure may be seen to the best advantage, and it 

 may be observed upon a smaller scale in the falls of Blea Beck. 

 Spreading from the Caldron as a centre, in our district the 

 Basalt ranges up Maize Beck for two miles, attains a consider- 

 able elevation above the river in Cronkley Scars, and may still 

 be seen in the river-bed as far down as the High Force and 

 Winch Bridge. At the High Force the top of the waterfall is 

 Basalt, and the lower beds indurated and subprismatic shale, 

 with beds of limestone below. Leaving the Tees lower down 

 it ranges along the south side of the dale past Holwick and 

 Unthank, and at last is lost about a quarter of a mile from the 

 Tees half a mile from its junction with the Lune. The whole 

 district is full of the marks of eruptive force and the influence 

 of great dislocations. Its four principal faults will be noticed 

 more particularly when we come to speak of the Yoredale 

 Rocks. From the upper part of Lunedale two basaltic dikes 

 pass near the end of the great basaltic mass, and are prolonged 

 in a north-eastern direction to the Durham coal-field. Although 

 there is in our district great uniformity in its geological position, 

 the fact that the beds above the great Whin Sill are altered as 

 well as those upon which it rests, shows that it is an intrusive 

 sheet. 



(6) The Yoredale Rocks. — The most characteristic section 

 of the upper mountain limestone series of strata is to be met 

 with in the upper part of Yoredale or (as it is now more comi- 

 monly called) Wensleydale, in the neighbourhood of Hawes. 

 In the fells upon both sides of the dale it reaches a thickness 



Jan. 1888. 



