116 THE LIASS1C PERIODS. CHAP. 



Upper lias clay, with Ammonites bifrons, A. heterophyllus, A. communis, and 

 Belemnites elongatus, 35 feet. 



Marlstone, solid and ferruginous, with Cardium truncatum, Rhynchonella tetraedra, 

 &c., 20 feet. 



Lower lias clay. 



Thus the relation of the oolitic and liassic beds from the great 

 oolite to the lower lias appears in one hill face of less than 150 

 feet. At Cheltenham the inferior oolite alone exceeds this thick- 

 ness, but near Oxford that rock seems to be untraceable. 



It is in the niarlstone, and in strata almost immediately above 

 .it, that the principal part of the liassic iron ore is found. Through 

 a great part of the deposit iron prevails, united with sulphur, or 

 with carbonic acid. Layers of nodules, often having the fissured 

 structure of septaria, occur in most parts of the lias clay, some 

 of which are calcareo-argillaceous, others calcareo-ferruginous. In 

 a general sense the prevalence of iron-carbonate augments as we 

 go northward ; it is not remarkable at Lyme Regis, and only 

 becomes prominent in the Oxfordshire district, where also the 

 higher ferruginous bed at the base of the inferior oolite is found 

 worth attention for the iron-furnace. The further north we go, the 

 more does the ferruginous quality of certain layers above the marl- 

 stone become conspicuous; till at length on the Yorkshire coast 

 nodular and bedded masses of iron ore appear, eight, eleven, and 

 even sixteen feet thick, and yield what promises to be an inexhaust- 

 ible supply. When of good quality, three tons of that ore will 

 produce one ton of iron. The marlstone itself is not worked for 

 iron in Yorkshire; but it appears to be only from its reduced 

 equivalent in Oxfordshire that the ore has been obtained. 



This rock, always arenaceous but rarely conglomeratic, is not 

 divided by bands of clay, nor are there any layers of limestone, 

 except where the shells (Pectines, Rhynchonellse, &c.) are so frequent 

 as to make of themselves a calcareous element. An example of 

 conglomerate in marlstone is given by Mr. Hull from a quarry 

 south of Daylesford, the pebbles being slaty and arenaceous, of 

 a Silurian aspect, not exceeding one inch and a half in diameter. 

 The marlstone is extensively used for building and tombstones 

 (Hornton, Chastleton). 



Among fossils which are frequent in the marlstone of the mid- 

 land counties, and occur about Banbury, Stow, and Cheltenham, 

 we have 



