486 TIDDEMAN : CARBONIFEROUS ROCKS IN UPPER AIRE-DALE. 
The strike, except in a contorted country, is generally very regular 
and continuous. On minute examination this rock is found to he 
full of Foraminifera, and fragments of other organisms in a state of 
disintegration, though perfect fossils of certain kinds frequently occur 
in it. It \vould be called by a geologist a distinctly well stratified 
rock ; it gives good regular features along its strike, and extends 
over wide areas. 
The white limestones south of the faults, on the other hand, 
are notable for their comparatively massive character and irregular 
bedding. They occur sporadically, rising into big mounds of conical 
form which usually rest on the black limestones. They contain great 
quantities of Ceplialopods, Bracliiopods, Lamellibranchs, Gasteropods, 
Corals, etc., and these are often in a wonderfully perfect state, and, 
from the way in which they compose the rock, appear to have lived 
and died on the spot. 
The general structure of these big mounds, or Knoll-Reefs, as I 
have called them, is very peculiar. They do not obey the rules of 
dip and strike which are usually found to obtain in ordinary parallel- 
bedded deposits, and any one seeking to apply these rules to them in 
mapping will be landed in numerous puzzles and difficulties. When, 
however, from the examination of several of them, the general 
structure is once mastered, their peculiar forms soon become easy of 
comprehension. Where they are quite perfect, a condition in which 
weathering has seldom left them, they are seen to consist of a Hat 
top, the dip of which usually agrees with that of the other rocks of 
the country around in every direction and angle of dip, and steep 
sides all round, the dip of which is away from the centre of the hill. 
This dip averages 30° to 35^, but may be much higher or lower, in 
proportion as the dip of these flanking beds is increased or lessened 
by the general dip of the country round. The dip of the flat at the 
top is a plane of deposition, which was once horizontal. The dip of 
the flanking beds represents on the other hand an original angle of 
deposit, plus or minus any subsequent tilting by movements of the 
crust. 
In other Knoll-Reefs, which have been cut into by weathering 
or quarrying, we And that the beds within, though sometimes obscure, 
