RICHARDSON : THE LOWER OOLITIC ROCKS OF YORKSHIRE. 191 
their equivalents, rest, where they are present, as a rule non- 
sequentiaU3\ upon a deeply-eroded surface of the Lias and that 
therefore the division-line between Lias and Oolites is usually 
sharply defined. 
The topmost sub-division of the Lower Oolites is the Corn- 
brash. 
In Yorkshire the Cornbrash has not been detected to the south 
of a line drawn in a westerly direction a little north of west from 
Filey ; but to the north thereof it has generally been found in 
its proper stratigraphical position wherever natural or artificial 
sections have been available. 
In this county it does not closely resemble lithically the deposit 
that bears the same name in the South-west of England. Instead 
of being mainly a bro^Mi rubbly limestone, it is principally shales 
with a median band of limestone, which is of a bluish colour on 
the coast, but everyAvhere ver}^ fossiliferous. The shaly beds 
above the fossiliferous limestone have been called the " Clays of 
the Cornbrash," and authorities have been diA^ded as to whether 
they should be classed with the Cornbrash or with the overlying 
Oxfordian. I would regard them as best grouped with the 
Cornbrash. 
It has also been questioned whether the Yorkshire Cornbrash 
is contemporaneous with the Cornbrash of other parts. Clydoni- 
cera^ discus (Sow.) does not appear to have been recorded from 
Yorkshire ; but specimens belonging to the genus Macrocephalites 
are not infrequent. More satisfactory correlations ma}', however, 
be accomplished with the aid of the brachiopods. Thus Mr. 
Buckman writes to me : — 
Taking the Cornbrash as consisting of the three zones : — 
(1) Macrocephalus, 
(2) Lagenalis, and 
(3) Intermedia 
the Yorkshire Cornbrash perhaps shows 1 and 2 mostly ; but the 
Dorset Cornbrash is more often 3. Zone 2 is found at places in 
Somerset ; zones 2 and 3 were found on the Badminton Railway ; 
and zone 2 is very fossiliferous at Fairford and again at Northampton. 
The Stilton rock is, I gather, mostly zone 3. The top zone (1) is 
finely developed at Garsden. near Malmesbury, Wiltshire ; but I do 
not know it in Dorset or Somerset. I know that its ammonites are 
fairly common in Yorkshire. 
