Intra-Jurassic Movements. 201 



attenuated near the anticlinal axes, and would be best developed 

 in the synclinal areas. 



The variations in the thicknesses of these zones \\'\\\ now be con- 

 sidered in order to see whether there exists any definite relationship 

 between such variations and the positions of the postulate folds. 



(1) Ac'utum Zone. — The acutuni zone is especially suitable for the 

 present purpose for several reasons. As the " Transition Bed " 

 between the Middle and Upper Lias, and containing many fossils, 

 it has received much attention. It has also been well exposed in 

 many workings for Marlstone Ironstone, while it is very thin and 

 its fossils easily recognized, so that there are few records that cannot 

 be utilized. 



The distribution of the deposits of acAiti age constitutes a striking 

 confirmation of the suggested folding.^ While the acutum zone is 

 well represented around Lincoln, it is probably absent at Grantham, 

 appearing again as a thin layer at White Lodge near Waltham-on- 

 the- Wolds, Leicestershire, in the Old Dalby syncline. In the neigh- 

 bourhood of the Melton Mowbray anticline the acutum zone has not 

 Ijeen recorded, a fact which makes it extremely probable that the 

 zone is not represented there. South of this region, hoAvever, in the 

 Tilton syncline, the zone attains its best development around Tilton. 

 It has again not been recorded anywhere in the neighbourhood of 

 the postulated Market Harborough anticline, and it is likewise 

 thin or absent along the line of the supposed Weedon anticline, 

 but its presence has been proved in the intervening district, which 

 includes what we propose for convenience to refer to as the Cold 

 Ashby syncline. 



Again, between Northampton and Banbury the acutum zone is 

 well seen, and has been described by- many observers at Chipping 

 Warden and Byfield. Towards the suggested anticline through 

 Banbury, however, the deposits again thin out, and at King's 

 Sutton a very attenuated re])resentative rests on an eroded surface 

 of Marlstone. West of this line the acutum zone once more thickens 

 in the region of the Edgehill syncline, but still further south or west 

 it has not been found. 



At several localities, such as Aston le Wall and Milton, situated 

 near the lines of the postulated anticlines, the deposits contain 

 rolled materials or pebbles, a further evidence of slight erosion. 



(2) The Tenuicostatiwi Zone. — The tenuicostatum zone (formerly 

 miscalled the annulatum zone) occurs at the base of the Upper 

 Lias immediately above the Transition Bed {acutum zone). In many 



^ The thicknesses of zones have been obtained mainlj' from the following 

 sources: Judd, The Geoloqy of RuUa7id, etc. (Mem. Geol. Surv.), 1875. 

 Walford, Proc. Warwick. Nat. Field Club, 1878, p. 37. Thompson, Journal 

 Northants Nat. Hist. Soc, vol. ii, 1882-3. Wilson & Crick, Geol. Mag., 

 1889, p. 296. Thompson and others in Report of Brit. Assoc, 1891, pp. 334-51. 

 Woodward, Lias of England and Wales (Mem. Geol. Siirv.1, 1893. 

 Richardson, Handbook to the Geology of Cheltenham, etc., 1904. Truen an, 

 Geol. Mag., 1918. pp. 106-8. 



