60 
HUGHES : INGLEBOROUGH. 
This is a very useful fact to bear in mind when mapping an 
area in which outcrops are scarce, and large boulders of cleaved 
rock common, where it is difficult to decide whether a mass 
which may be important for geological mapping is rock in place 
or merely an eartji-bound boulder. If cleavage is visible, and 
is not normal, the chances are that it is not rock in place. Varia- 
tions from the normal in direction or inclination are apt to 
occur where massive rocks not susceptible of cleava,ge occur 
among others in which molecular rearrangement can be pro- 
duced. In such cases the tough massive rocks are thrown 
into folds, to which the soft compressible materials of the slates 
have to accommodate themselves. 
The Horton Flags creep out in a synclinal fold from under 
the Mountain Limestone of Studrigg Scar. They pass down 
through thin bedded grits and roughly cleaved shales into the 
Austwick Grits, whose lighter colour is conspicuous in " White 
Stone," the name of the steep rocky ground on the south. The 
axis of the synclinal falls to the east, and, as its centre deepens, 
the northern and southern limbs spread further apart under 
the Carboniferous rocks of Moughton, so that the flags occupy 
a mile from north to south along the v/est side of the Ribble, 
and on the east side the synclinal opens out still more as the 
Silurian rocks disappear under the Mountain Limestone. 
Seeing that the Horton Flags are the most important 
member of the Silurian rocks of this district, it may be con- 
venient to describe here the three sections, which I have drawn 
to illustrate the Silurian succession in the adjoining valleys of 
Crummack Beck and Ribblesdale, although the sections carry 
us above and below the horizon which we have most especially 
under consideration. 
The reader is supposed to be looking east (Fig. 6), so that the 
south end of the section is on his right hand. Here we see the Bala 
Shales (g), with subordinate ashes and calcareous bands {g'), 
which have been previously described. Near the barn in the line 
of this section, Orthis retrorsistria McCoy, Leptoena transversalis 
Wahl., Trinucleus seticornis His., Illcejius davisii Salt., and Caly- 
mene blunienbachii Brong. were found. Further north we pass 
over the broken ground by the waterfall, the details of which 
