180 DAVIS : SECTIONS IN THE EIASSIC AND OOLITIC ROCKS OF YORKSHIRE. 
(The last three beds make a strong scar and well- 
marked line in the cliff). 
Shale, with remains of Pentacrinus tuberculatus, Belem- 
nites acutus, Modiola acutus. At the base is a row of 
small doggers containing A. gagateus in great num- 
bers, also A. oxynotus ... ... ... 7 3 
Shale, soft and dark, with fossiliferons nodules ... 6 0 
Below this the beds are not easy to trace ; there are 
probably about 40 feet of shales with harder bands. 
The zone of Ammonites Jamesoni (c) is composed of similar strata 
to those already mentioned. Their upper boundary is marked by the 
disappearance of Pinna folium and Am. Jamesoni. Apecularity of 
this zone is that the lines of doggers, especially in the lower beds, are 
replaced by bands of iron pyrites in imperfect tetrahedra ; many of 
the fossil Ammonites are composed entirely of iron pyrites. The beds 
form a large flat expanse of scars north-east of Baytown ; fossils occur 
in them either singly or more frequently in small conical heaps con- 
sisting of the shells of Pecten, Belemites and Gryphwa, a feature 
which characterizes this part of the Lower Lias. Pinna folium occurs 
throughout the series ; A. Jamesoni and A. brevispina occur chiefly 
in the upper beds ; and A. armatus and A. densinoides are common 
in the lower, in addition to Lima pectinoides, Inoceramus dubius, 
Pleuromya galethea, &c. The thickness of the strata of this zone is 
about 186 feet. Besides the location already given they may be 
studied in the base of the high cliff of the north-west side of the 
great Peak Fault. The strata is also exposed in the sides of the 
small streams flowing to Robin Hood's Bay, such as Mill Beck. 
The upper bed of the Lower Lias, the A. capricornus zone (d ), 
consists of 140 feet of grey micaceous shale, light coloured and sandy 
in the upper part, in the lower darker coloured and more argillaceous. 
A characteristic feature is the occurrence of bands of septariated 
doggers containing zinc blende at intervals of a few feet. In many 
horizons the Ammonites are casts entirely composed of zinc blende, 
and can be traced for considerable distances. Two of these bands, 
about fifty feet below the top of the Lower Lias, may be traced in 
the beds at Staithes and followed thence to Saltburn ; the upper one 
