BRITISH AVONIAN CONODONT FAUNAS 27 
Moore (1958 : 95) described the major limestone at the base of the cyclothems and 
grouped the other beds of the cyclothems together under the term “‘ Non-Calcareous 
Measures’’ (although they sometimes contain thin limestones and calcareous shales). 
The lower boundary of the Yoredale Formation in the type area was placed by 
Moore at the base of a thin sandstone-shale sequence, the Thorny Force Sandstone, 
which lies below the Hawes Limestone. As pointed out by Walker (1964 : 210) 
this lowest cyclothem is poorly exposed and is confined to a small geographical area. 
The Girvanella Bed, which is accepted as the D;—D2 boundary and hence roughly as 
the Bz—P;, boundary of the goniatite sequence, in the middle of the Hawes Lime- 
stone, is in this study taken as the base of the Yoredale Formation. 
The Hawes Limestone, which is forty feet thick, may be divided into two distinct 
members, a lower group of pale grey massive limestones, with pseudobreccias and a 
fauna of compound corals, and an upper group of blue-grey thinly bedded limestones 
with few fossils. The boundary between the two is the Girvanella Bed, which 
lithologically is part of the upper group. 
The Gayle Limestone, fifty-seven feet thick, may be divided into three parts. At 
the base is a group of wavy-bedded limestones with irregular shale partings. A 
massive bed, comparable in thickness to the whole of the underlying thin beds, forms 
the middle group. The upper part of the Gayle Limestone consists of massively- 
bedded, blue-grey, poorly-fossiliferous limestones. 
The Hardraw Scar Limestone, twenty-five feet thick, consists in the lower half of 
massive crinoidal limestones, often six feet thick at the base, which pass upwards 
into thinly-bedded, calcite mudstones. The upper part of the Hardraw Scar Lime- 
stone is more uniform than the lower, consisting of massive crinoidal limestones with 
partings of rubbly limestone, which pass up into finer-grained limestones and fine- 
grained calcite mudstones, which are partially dolomitised. 
Limestone III A is a fine-grained limestone containing corals (Lithostrotion). 
Limestone III B is arenaceous and almost unfossiliferous, whereas Limestone III C 
is less sandy and contains small crinoids. 
The Simonstone Limestone, which is fifteen feet thick, consists in the lower part of 
a clastic limestone phase, with the development of coarse crinoidal limestones and 
sandy limestones with a sporadic fauna at the base, which passes upwards into a fine 
grained limestone and calcareous shale facies which often contains compound corals. 
The upper part of the Simonstone Limestone consists of fine grained limestone at the 
base, overlain in turn by coarsely crinoidal limestones and fine grained algal lime- 
stones. 
Limestone IV A, three feet thick, is a fine grained limestone, which is sandy at the 
base. Limestone IV B is a fine grained argillaceous limestone, 23 feet thick, with a 
9” bed of shale in the middle. 
The Middle Limestone, 65 feet thick, is divisible into three thick limestone units, 
each separated by shales and thin limestone bands. 
The Five Yard Limestone, two feet thick, consists of fine grained limestones, 
sparingly crinoidal, but with a rich fauna of corals and brachiopods. This formation 
