part tt] jUEASsic chronology. 403 



Table II records the faunal contents of tlie Junction-Bed at 

 three places — I have drawn upon Mr. Jackson's evidence for one 

 date {suhcarinatum) in regard to Watton Cliff, — and it shows 

 that, while there is substantial agreement between sections of the 

 Western Cliffs and of Bothenhampton, 3^et that Watton Cliff 

 differs considerably from both. This divergence is more noticeable 

 than a mere list of fossil contents would indicate ; for the points 

 that are most strikingly in contrast l^etween Watton Cliff and the 

 other sections are, so far as Watton Cliff is concerned, 



(1) The continuity through most of the Watton Bed of white-stone 



deposits. 



(2) The considerable thickness of strata in which forms of Grammoceras- 



striatulum type are found. 



(3) The presence of the Thecidellse and u.nfamiliar Hildoceratids. 



(4) The absence of the Marlstone-Rock bed — serrata and associated beds. 



(5) The presence of tliQ Tetrarliynchia-tfiorncombiensis Bed and many 



derived examples of that fossil. 



These points are illustrated in Table II and diagrams 6 & 7. 



The section at Bothenhampton is near a line of fault, parallel 

 to and north of the Watton Cliff (Eype) Fault, heading in the 

 direction of Thorncombe Beacon, The Junction -Bed of Bothen- 

 hampton reproduces the Thorncombe type, and shows Marlstone 

 at the base. The Junction-Bed of Watton Cliff is closer to the 

 axis of the Weymouth Anticline, and shows not only denudation 

 and destruction of the Marlstone, but denudation carried down 

 many feet lower — to below the TetrarhyncJiia-tJiorncomhiensis 

 Bed (diagram 6, p. 402). 



Now, Day's measurements (see above, p. 397) were made at Down 

 Cliffs, 1 and by the increase in thickness it can be estimated that 

 his exposure was some 4250 feet — approximately 6 furlongs — 

 to the west of mine ; it would, owing to the trend of the coast, 

 take him some distance farther away from the axis of the 

 Weymouth Anticline, and this would account for the greater 

 thickness which he obtains between the Junction-Bed and the 

 margaritatus bed. The following sections (diagram 8, p. 404) 

 are placed in order from west to east, which direction, though not 

 at true right angles to the anticlinal axis, is sufficient to illustrate 

 the effect of it. 



Thus in the Down-Cliffs section, as there are some 92 feet 

 between the Junction-Bed and the margaritatus bed, in the 

 middle section about 68 feet, and at Watton Cliff about 40 feet, 

 the Tetrarhynchia-thorncomhiensis Bed must Imve disappeared 

 in the post-Marlstone denudation immediately east of Thorn- 

 combe Beacon, and the denudation has, at Watton Cliff, been 

 carried down into the ^Ye-TetrarJigncJiia-tJiorncomhiensis-^ed 

 Sands (diagrams 8 & 9, pp. 404, 405). 



The Marlstone Rock is only preserved at Thorncombe Beacon — 



^ There is reason to think that he took details, if not measurements, from 

 Doghus as well as from Down Cliffs — the latter name originally covered both. 



