52 
HUGHES : INGLEBOROUGH. 
side of Ingleborough, can be most probably accounted for, 
but, from the character of the material over the whole district, 
I hardly think that they can have thinned out here and there- 
fore offer the above diagram as the most probable solution. 
There still remains the discrepancy between the small 
thickness of what for convenience we cut off at Austwick under 
the name Pale Slates, and the enormous development of the 
similar beds in Spengill. In Spengill, however, we have not the 
Austwick Flags with subordinate grits, or the grits of the " White 
Stones " with their subordinate flags, and it may be that further 
palaeontological evidence may enable us to explain the difference 
in the sediments of the two areas on the hypothesis that the 
" Pale Slates " of Spengill have been developed at the expense 
of, and are equivalent to, part of the Austwick Grits and Flags. 
The Pale Slates. 
These are on the horizon of the Tarannon Shales of which 
Ramsay writes (Mem. Geol. Survey, vol. iii., 1866, p. 4). 
" The Tarannon Shales underlie the Denbighshire Sand- 
stones, and by the Geological Survey were first considered to 
form the uppermost part of the Bala Beds, but when the maps 
were nearly completed, Mr. Aveline began to suspect that they 
belonged rather to the Denbighshire Sandstone Series, a sus- 
picion entertained by Mr. Jukes before ; and I believe at a much 
earlier date Professor Sedgwick had mentioned them as pale- 
coloured earthy slates or ' paste-rock.' " 
They were described by Harkness and Nicholson (Q.J.G.S., 
xxxiii., p. 477, and named by them Knock Beds, on account of 
their excellent development in Swindale Beck, near Knock. 
The fossils which they record from them are— 
Monograptus priodon. 
M. hroughtonensis Nich. 
Orthis. 
Discina, 
and some minute lamellibranches. 
Miss EUes, to whom I am indebted for the revision of all 
my lists, is of opinion that the graptolite which appears above 
as M. priodon is probably the M. Marri of Perner. 
