THE HIGH FORCE, TEESDALE. 469 



level as that of the underflow at the Force, and the shale parting, 

 which at first makes its appearance somewhat abruptly, can be seen 

 for a dozen yards or so gradually thickening as we follow the bank 

 of the river in a north-easterly direction. The section then be- 

 comes lost, owing to the covering of tumbled whin, &c, and we have 

 to go on for some 70 yards before the beds are well shown again. 

 Here the section is much the same as that at Y, viz.: — 



Basalt. 



Shale, about 20 feet. 



Limestone. 



We have, then, good evidence that the section at X changes to- 

 wards the north-east in the same way as it does towards the south- 

 west and south. 



And so, finally, we see that near X a small part of the lower por- 

 tion of basalt becomes separated off from the main mass, and that 

 this lower portion rapidly thins out towards both the south-west and 

 south, and the north-east. 



There are other places, both in the immediate neighbourhood of 

 the High Force and elsewhere, where similar undoubted underflows 

 exist. Sometimes these underflows can be seen distinctly in the act 

 of being gradually separated off from the main basalt mass, altered 

 beds coming in between ; and sometimes these altered beds consist 

 of altered sandstone, or of altered limestone, instead of altered shale. 

 And, as there are underflows, so also there are overflows ; parts of 

 the top of the basalt gradually get separated off from the main mass, 

 and then thin out. 



In some cases we can see beds of altered shale and sandstone 

 apparently surrounded by basalt on every side : there is basalt above ; 

 and there is basalt below ; and the altered beds can be seen to end 

 in basalt as you follow the section along on either hand. There is 

 a very good instance of this in the Slate Scar, a little more than half a 

 mile above the High Force. The greatest dimensions of these beds 

 are seen to be generally in the direction of their planes of original 

 deposition ; their thicknesses are, in fact, generally strikingly less 

 than their length. For instance, with an average thickness of 2 

 feet, we may get a length of 60 yards. This is, I think, strongly 

 suggestive of some stable connexion between these and the other beds 

 among which the basalt has been intruded ; they appear to have 

 kept something of their original position very much better than one 

 would suppose at all likely if they had been completely isolated in the 

 great basalt mass. I would suppose, then, that, certainly in most 

 cases, these beds are not surrounded by basalt on every side — have 

 not, in fact, been simply " caught up " in it — but that, if they could 

 be traced in directions both away from the observer and towards 

 him, they would, in one of these directions, be found to join on with 

 the great mass of the sedimentary rocks of the country. It is evi- 

 dent that, in any ordinary section, we have only four sides visible 

 out of the six wherewith any geographical point may be supposed 



