Intra- Jura ssic Movements. 



203 



* Denotes zone present. 



For instance, the planorbis zone in the Old Dalby syncline shows 

 a characteristic thickening from Owthorpe and Cotgrave Gorse on 

 the north to East Leake, near the synclinal axis.^ ' Further south 

 ^again, at Barrow-on-Soar, the zone is again thinner. These facts 

 are extremely suggestive of movement along the axis in Lower 

 Liassic times, but unfortunately no details of this zone are available 

 further south. 



The chief lack of information concerning many zones is due to the 

 broad way in which they have been interpreted. Minute zonal 

 studies on the lines indicated by Mr. Buckman's recent work ^ 

 cannot fail to yield a great deal of useful information, for in many 

 cases the zones he defines are so thin and have a fauna so distinct 

 that given sufficient exposures it will be a comparatively easy matter 

 to trace their extent. 



Meanwhile it has only been possible to collect isolated facts, but 

 some of these are significant. For example, the capricorns of the 

 Liparoceras series, which mark a definite but comparatively short 

 period of time, have only been found at Dumbleton and Napton-on- 

 the-Hill, Warwickshire, both of which are situated on supposed 

 synclinal lines. '^ 



(4) Other Types of Evidence. — Working on the same principle, 

 attempts were made to trace any relationship between the folds and 

 the thicknesses of the strata, using the total thickness of whole 

 formations. The attempts were unsuccessful, partly on account of 

 the few data available, there being a surprising lack of records that 

 give, for instance, the total thickness of the Lower or Upper Lias ; 

 further, the small variations that may be expected as a result of any 

 contemporaneous folding are superposed on large-scale regional 

 variations due to regional tilting, or to secular elevation which was 

 m progress at the time of deposition. For instance, during Toarcian 

 (Upper Lias) times the area of maximum deposit moved southwards 



' Trueman, Geol. Mag., 1918, pp. 67-70. 



' Buckman, "Jurassic Chronoloo;v : I. Lias": Quart. Journ. Geol. Soc, 

 vol. Ixxiv, 1919. 



^ Trueman, "The Evolution of the Liparoceratidaj " : Quart. Journ. Geol, 

 Soc, vol. Ixxiv, 1919, p. 2.52, etc. 



