68 
HUGHES : INGLEBOROUGH. 
Our list, therefore, represents only one horizon near the 
base of the 2,000 feet of Horton Flags, but it is probable that 
zones characterised by a different facies may be made out in 
such a thickness even of fairly uniform sediment. A beginning 
might be made by comparing the fossils of Arco Wood with 
those of Combes Quarry, which is much higher in the series. 
Orthoceras. 
The Orthoceras primcevum is the fossil described under the 
name Creseis primceva by Ed. Forbes* who, in both cases, refers 
to the longitudinal grooves so commonly observed in the 
flattened specimens. McCoy, f however, in 1855, pointed out 
that the longitudinal groove was only a crush in the last chamber, 
and Salter,! in 1873, described it as " easily crushed." The 
tendency to break in this manner is obviously a characteristic 
of the species. 
The other common Orthoceras is evidently that described 
by Forbes II as Creseis Sedgwickii, which was considered by 
Salter § to be the same as Orthoceras tenuicinctum of Portlock. 
The Studfold Sandstone. 
The anticlinal axis referred to above in describing the 
surface extension of the Horton Flags still falls to the east, 
so that on the east side of Ribblesdale the centre of the fold 
is still further depressed and the northern and southern base 
of the series are nearly two miles apart. In the centre of this 
anticlinal, which has here a double fold, the next overlying series, 
namely, the Studfold Sandstone, comes on above the Horton 
Flags just as the Horton Flags themselves crept out in a synclinal 
fold over the Austwick Grits in Crummack Dale. We have thus 
the whole thickness of the Horton Flags represented in 
Ribblesdale. 
♦Q.J.G.S., vol. i., (1844), p. 146, fig. 1, and vol. ii., p. 314, PI. 
XIII, fig. 2. 
+ Synopsis, &c., Sedgwick and McCoy, p. 31C. 
X Salter Catalogue, Camb. Sil. Foss., p. 159. 
II Op. cit., p. 146. 
§ Op. cit., p. 158. 
