MIDDLE LIAS. 2/3 



town and Banbury. Above the Marlstone Rock-bed there are 

 thin beds of marly limestone and clay, characterized by Ammonites 

 acutus, and containing A. Holandrei, but also many fossils of a 

 Middle Lias character; and Mr. E. A. Walford, while noting it 

 as a ' Transition-bed,' is inclined to group it with the Middle Lias, 

 and as perhaps synchronous with the zone of Ammonites anjiiilatus 

 of Messrs. Tate and Blake, in Yorkshire. (See p. 258.) The Rock- 

 bed, about 6 feet in thickness, is underlaid by marly clays and soft 

 sandy limestone, about 12 feet thick, and these constitute the zone 

 of Ammonites spinatus; below are marls and clays with sandy lime- 

 stone, about 26 feet, which represent the zone of A. margaritatus. 

 The beds, which are variable in character, may be seen at Bugbrook, 

 Daventry, Byfield, Chipping Warden, Chalcomb, Milton, Staverton, 

 Middleton Cheney, King's Sutton, etc. Trigonia Lingonensis has 

 been obtained at Aston-le-Wall and Appletree. Mr. Beeby Thomp- 

 son observes that the zone of A. margaritatus is characterized by 

 Lamellibranchs, that of A. spinatus by Brachiopods, and the 

 Transition-bed by Gasteropods.' In Warwickshire the Middle 

 Lias (Marlstone) forms Edge Hill, south-west of Kineton. 



In Rutlandshire and Leicestershire the Marlstone or Rock-bed 

 varies much in thickness, attaining a maximum of about 30 feet ; 

 being about 18 feet at Tilton-on-the-Hill, and diminishing to 

 8 or 9 feet near Oakham. Belvoir Castle is situated on an outlier 

 of Marlstone ; Blackberry Hill to the west is capped by the same 

 rock. 



By the Railway Station at INIarket Harborough the Marlstone 

 rock-bed (isin.) is underlaid by clays with nodules containing 

 specular-iron. Protocardinm triincatiim, Avicida cygnipes, etc., occur. 

 Slawston Hill is an outlier of Marlstone, capped by Upper Lias 

 Clay and Northampton Sand. At Robin-a-Tiptoes Hill the Rock- 

 bed is nearly twenty feet in thickness, and at Melton Mowbray it is 

 thirty feet. The lower part of this bed, of a greenish-blue colour, 

 is largely made up of specimens of Terebratida punctata and Rhyn- 

 chonella tetrahedra. The blue ferruginous sandstone, by weathering 

 passes into a friable brown sandstone, owing to its carbonate of iron 

 being changed into peroxide of iron under the influence of air and 

 water.'^ 



In north-west Lincolnshire the Marlstone is but eight feet in 

 thickness, the lower beds comprise about sixty feet of clay. 

 Between Leadenham and Lincoln the Marlstone is not represented 

 as a rock-bed, but it re-appears at South Carlton, north of Lincoln. 

 Clays with A. margaritatus may be seen in brickyards south of 

 Lincoln.^ (See Fig. 42.) To the north of Lincoln Mr. Ussher has 



1 Walford, Proc. Warwick Nat. Hist. Club, 1878; and Thompson, Midland 

 Naturalist, 18S5-1886. 



^ W. J. Harrison, P. Geol. Assoc, v. 142 ; see also E. Wilson, The Lias 

 Marlstone of Leicestershire as a source of Iron (reprinted from the Midland 

 Naturalist, viii. 61, etc.) ; Beeby Thompson, Midland Naturalist, viii. ; and P. B. 

 Brodie, Proc. Cottesw. Club, i. 59. 



^ W. D. Carr, G. Mag. 1883, p. 164 ; P. Geol. Assoc, viii. 383. 



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