THE HIGH FORCE, TEESBALE. 



467 



out by what can be seen of the physical disposition of these beds in 

 the grounds immediately adjoining the High Force. 



What a very great difference there is between b and c and between 

 c and d is evident at once from a first look at the Force — b and d 

 being conspicuously crossed by lines of lamination rudely parallel 

 to their upper surfaces, while c is completely without any such lines, 

 and is rudely prismatic, like the basalt at the top of the Force. But 

 these differences are seen to be, if possible, still greater when we 

 come to examine the Force, and the minuter structure of the beds : 

 b and d have no trace of crystalline structure whatever, while a and 

 c both have, and the structure of c appears to agree exactly with 

 that of the lower part of a. Both c and the lower part of a are much 

 more finely crystalline than the more centrally situated parts of a ; 

 but this is only what one would expect on considering the different 

 conditions under which their cooling would probably take place. The 

 outside of the mass would naturally cool much more quickly than 

 the inside ; and the underflow, c, is only about 6 feet thick, and 

 therefore the whole of this would probably cool down comparatively 

 quickly. 



I think, then, that there can be no doubt that the bed c is really 

 basalt (microscopic examination would prove this), here a sort of 

 underflow to the main mass. For Phillips's section I would substi- 

 the following: 



Fig. 1. — Section at the High Force. 



"am 



a. Basalt, 24 feet. d. Shale, altered, 12 feet. 



6. Shale, altered, 1£ foot (average). e, f, g. Limestone, 32 feet. 



c. Basalt, 6 feet (average). 



The thicknesses given are only approximate. 



