DAVIS: SECTIONS IN THE LIASSIC AND OOLITIC ROCKS OF YORKSHIRE. 187 
L. rugosus. 
A. elegans, Sow. 
L. pectinatus. 
A. aalensis 
Pachycormus curtus. 
A. serpentinus, Rein. 
P. latirostris. 
A. exaratus. 
P. gracilis. 
A. caecilia. 
P. latus. 
A. subconcavus. 
P. macropterus. 
A. lineatus. 
P. acutirostris. 
A. cornucopia. 
P. latipennis. 
A. erratus. 
Ptycholepis bollensis. 
Natica buccinoides. 
Leptolepis saltviciensis 
Discohelix rainutus. 
Aspidorhynchus anglicus. 
Inoceramus dubius. Lon. 
Belonostomus acutus 
I. Simpsoni. 
Beloteuthis subcostatus. 
Tancredia dubia. 
B. Leckenbyi. 
Posidonomya Bronni, Voltz. 
Groteuthis coriaceus. 
Pecten pumilus. 
Teudopsis cuspidata. 
Monotis substriatus. 
Belemnites tubularis. 
Pleuromya bituminosa. 
B. inaequistriatus. 
Ceromya exarata. 
B. dorsalis 
Modiola Simpsoni. 
B. crossotelus. 
Protocardium substriatulum ? 
B. voltzii, Phill. 
Discina reflexa 
B. breviformis. 
Extracrinus briareus. 
B. striolatus. 
E. dichotomus. 
B. laevis. 
Pachyphyllum peregrinum. 
B. acuminatus. 
B. scabrosus. 
The Alum Shale, the uppermost of the Liassic Series, is 
first seen rising from the bed of the sea at Blea Wyke, capped by 
some soft sandy shale. The thickness is about 150 feet. The upper 
100 feet is a soft grey micaceous shale, which weathers to small 
crisp fragments with yellow edges. This is the source of the alum. 
The rocks are characterized throughout by the presence of A. com- 
munis and Leda ovum. The lower 50 feet are harder and darker 
bituminous shales, not used for alum, in which ammonites of the 
serpentinus type predominate. The Alum Shales form the lower part 
