Vol. 58.] GAPS IN THE LIAS. 267 
15. On some Gavs in the Liss. By Epwin A. Watrorp, Ksq., 
F.G.S. (Read February 26th, 1902.) 
Tus calcareous beds of the Middle Lias attain a maximum thickness 
near Banbury in Oxfordshire. They form the highlands of the 
escarpment (the outcrop) on the North Oxfordshire border at their 
highest altitude, 720 feet above Ordnance-datum. 
The several zones of the Middle Lias may be put broadly into 
three lithological divisions :— 
1. Zone of Ammonites spinatus, and Transition-Bed. (Calcareous.) 
2. Zone of Ammonites margaritatus. (Argillaceo-calcareous.) 
3. Zone of Ammonites Jamesoni or ibex and Amm. capricornus, (Argillaceous.) 
The deposition of divisions 2 and 3 followed a long period of 
sedimentation, mainly of argillaceous type. They are, in fact, 
repetitions of the previously existing conditions of the Lower Lias, 
differing only in a gradual increase in the thickness of the argil- 
laceous limestones towards the top of the zone of Ammonites mar- 
garitatus. Similar conditions prevailed over the whole of the 
English Liassic seas. Though the incoming of the zone of Amm. 
spinatus was with some argillaceous deposit, the true zonal type 
was reached in the calcareous bands at the base of the great [ron- 
stone Series, wherein the true fauna of the zone rests. In the 
Midlands and in Yorkshire these limestone-beds are at the lowest 
part of the. 30 feet of rock and clay of the Amm.-spinatus zone. 
Nodular and concretionary bands characterize them. The nodular 
limestones are represented in Somerset, Dorset, and Gloucestershire 
by marly limestones yielding also the molluscan fauna of that part 
of the zone. 
The ferruginous limestones of the superior part of the zone I 
have elsewhere * shown to be mainly a sub-crinoidal bank of great 
thickness and importance in Northern Oxfordshire and Cleveland 
(Yorkshire), both now important centres of the iron-industry. 
Hence the zone of Anmonites spinatus may be divided into an 
upper and lower series :— 
Feet 
Zone of 1. The Ferrocrinoid-Beds (superior) ...... 30 
Amm. spinatus. | 2. The Spiriferina-oxygona Beds (inferior) 20 
Variations in thickness of the superior division in Oxfordshire are 
frequent, ranging from 30 feet (at an altitude of 700 feet) to 6 feet 
~on the edges of the Cherwell Vale (at an altitude of 350 feet), 
owing to waste by water-flow. 
Special or abundant fossils of the Ferrocrinoid-Beds (1) :— 
Ammonites spinatus (very rare). Terebratula punctata. 
Rhynchonella tetrahedra, LT. Edwardsi. 
Eh. tetrahedra, var. northamp- ‘aldheimia indentata. 
tonensis. Ferrocrinoids. 
* *On the Making of the Middle Lias Ironstone of the Midlands’ Journ. 
Tron & Steel Inst. vol. xlix (1896) p. 74. 
