RASTALL : THE INGLETONIAN SERIES OF W. YORKSHIRE. 89 
admirably displayed at Thornton Force in Kingsdale. On the 
eastern side of the Chapel-le-Dale valley there is an exposure of 
this unconformity which is of classic interest, since it was 
described as long ago as 1802 by Playfair in his " Illustrations 
of the Huttonian Theory." 
As will be seen by reference to the map, the greater part 
of the area in question is occupied by an alternation of slates, 
flags, and grits, the Ingletonian series proper, but at the S.W. 
end, close to the fault, there is a narrow strip of calcareous 
rocks, impure limestones and shales, which are correlated with 
the Coniston Limestone of other districts. The rocks are much 
crushed and cleaved, so that fossils are difficult to extract. 
However, sufficient have been obtained to show that these 
beds are at any rate of Upper Ordovician age, probably Cara- 
docian. The bedding is so much contorted and the junctions 
are so obscure that it is impossible to say whether these calcareous 
beds are conformable with the Ingletonian rocks or not. Litho- 
logically they strongly resemble the corresponding strata of 
Edenside and the Lake District. Even at Horton, where the 
succession is much clearer, it is impossible to prove conformity 
or otherwise, owing to faulting and folding. Intruded into the 
Coniston Limestone of Ingleton are two or more lamprophyre 
dykes, which are of no great interest, as they are much de- 
composed. One of them is very well seen forming a barrier 
across the river a short distance above the fault, and close to 
this is another dyke of a more acid character, which may be 
described as a felsite. 
All the rest of the area in question is occupied by a succession 
of slates, flags, and grits, usually of a greenish colour, and on 
the whole of remarkably uniform character. The total length 
of the exposure is over two miles, and as the dips are very high, 
usually approaching the vertical, the total thickness of rock 
exposed must be not far short of 10,000 feet, assuming that 
there is no repetition. It has been suggested by several authors 
that repetition by folding or faulting is at any rate a possibility 
to be considered. Professor Hughes's remarks on this point 
are very cautious and non-committal.* As was before pointed 
*Geol. Mag., 1867, p. 346. 
