GEOLOGY 



JURASSIC 



The Lower Lias succeeds the Rhastic without any marked inter- 

 ruption ; locally there may have been some little breaking up of pre- 

 viously formed beds, brought about perhaps by changes of current, but 

 on the whole the Lias came in quietly. The formation occupies much 

 of the southern part of the county. The basement beds consist usually 

 of even-bedded blue limestones and dark shales in thin alternating bands ; 

 certain of the limestones and others which belong to the underlying 

 White Lias contain numerous remains of insects and have long been 

 known through the researches of Brodie as the Insect Beds. Throughout 

 the Warwickshire area the beds are especially rich in species of the 

 lamellibranchs Cardinia and Hippopodium, and the lowest layers abound 

 in the small oyster Osfrea liassica. But it has been found that the 

 ammonites more than any other fossil exhibit a succession of species 

 each of which characterizes a certain part of the formation ; and we 

 thus are enabled to subdivide the Lias into a number of ' zones," of 

 which the lowest is that of Ammonites planorbis. In the district between 

 Evesham and Stratford-on-Avon many sections of the A. planorbis beds 

 have been described, notably by Mr. R. F. Tomes, the Rev. P. B. Brodie 

 and Dr. Wright. At Binton the lowest layer, known as the Guinea 

 Bed (see p. 17), by its peculiar character seems to imply some amount of 

 local interruption in the processes which deposited the lowest limestones 

 and clays of the Lias, which usually follow the Rhastic without any 

 break. At Wilmcote the lowest beds have been extensively quarried 

 and have yielded A. planorbis, A. jo&nsfoni, the crustaceans Glyphea and 

 Eryon and also bones of saurians. 



The Lower Lias limestones are exposed in the railway cuttings 

 between Stratford-on-Avon and Eatington and were described by Brodie. 1 

 Near the station north of Upper Eatington, beds characterized by abun- 

 dant specimens of Lima are exposed in a cutting some 60 feet deep ; 

 and at Kineton the cuttings show limestones and shales containing among 

 other fossils A . angu/atus, Gryphaa arcuata and several species of Lima ; 

 the beds here evidently belong to the zone of A. angu/atus, which 

 succeeds that of A. planorbis. 



At Harbury are extensive lime and cement works in the same zone. 

 In the adjacent railway cutting it appears that the zone of A. planorbis^ 

 usually rich in limestone bands, is represented by about 30 feet of blue 

 clays and shales; 2 the overlying limestones have yielded remains of the 

 saurians Ichthyosaurus and P/esiosaurus, the fish Acrodus, several species of 

 ammonites, including A. bucklandi^ together with lamellibranch shells and 

 crinoids. Beyond Harbury the limestones of the zones of A. angu/atus 

 and A. bucklandi have been wrought at numerous localities towards 

 Rugby. 



The highest beds of the Lower Lias were formerly well exposed in 

 the railway cutting south of Fenny Compton station, and have been 



> Quart. Jout-n. Gtol. SK. xxx. (1874), 746. Woodward, op. cit. pp. 159, 160. 



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