400 STKATIGKAPHICAL GEOLOGY 



( Ferruginous limestones with Arnioceras semicostatum. 

 Lower Lias, | Blue clays and grey limestones (Coroniceras Bucklandi}. 

 A ~\ Dark-blue pyritous clays (Schlotheimia anyulata). 



^Limestone and shales (Psiloceras planorle). 



The zones of planorbe, angulata, and Bucklandi present the 

 same features as elsewhere, and have a combined thickness of about 

 200 feet. They are succeeded by several beds of hard ferruginous 

 limestone with interbedded shales (the semicostatum zone), which 

 thicken northward till they are 27 feet thick at Scunthorpe and 

 Frodingham, where they are worked for ironstone. 



The upper part (B) of the Lower Lias is about 470 feet thick 

 in the Vale of Belvoir, and a boring at Granthani showed the 

 Lower Lias as a whole to be about 700 feet thick. The obtusum 

 zone is thin or absent, but clays \\iihoxynotum and raricostatum occur, 

 and are about 90 feet thick. Northwards, however, the thickness 

 diminishes. The lower zones (A) maintain their thickness, but 

 the zones of oxynotum, armatum, and Jamesoni are represented by' 

 clays from 100 to 140 feet thick, surmounted by a bed of ironstone 

 about 4 feet thick, which is known as the " Pecten Bed," from the 

 abundance of several species of Pecten. This bed contains a 

 mixture of Lower and Middle Lias species, and is by some regarded 

 as the base of the Middle Lias, but its Ammonites are armatum, 

 Henleyi, and striatum, while the clays above it contain JEgoceras 

 capricornus throughout and not Amaltheus margaritatus. These 

 clays are about 70 feet thick, and consequently the total thickness of 

 Lower Lias in this district is from 400 to 440 feet. 



Middle Lias. In the counties of Oxford and Warwick the 

 Middle Lias is about 150 feet thick, and Mr. H. B. Woodward 

 remarks that " the Marlstone Rock-bed is perhaps nowhere better 

 developed than in the country around Banbury. It covers an 

 extensive area to the north-west, forming a plateau that rises 

 gradually from about 500 feet at Banbury to the escarpment of 

 Edge Hill, 710 feet high, and this area is intersected by several 

 deep valleys." The Marlstone consists of more or less ferruginous 

 and sandy limestone, which varies from 12 to 25 feet in thickness. 

 The outer parts are always brown from the oxidation of the iron, 

 but the centres of large blocks are generally grey. The commonest 

 fossils are Terebratula punctata and Rhynchonella tetrahedra, which 

 often occur in clusters. 



Upper Lias. This division is well developed in North- 

 amptonshire, where it has been studied and described by Mr. B. 

 Thompson. 6 He divided it into 8 zones, but the highest of these 

 forms a passage into the overlying series, and would perhaps be 

 better included in the latter ; his 7th zone is a nodule bed at the 



