part 4] JURASSIC CHEONOLoar. 389 



horizon tall}'. A striate Nautilus of fair size was obtained from 

 just below the [lower?] sfriatulum layer and a little ZeiUeria 

 (the so-called ' Widdheimia lycetti'') was obtained from this 

 striatulum layer. 



A comparison of this detailed section of the Watton Bed with 

 that of the Junction-Bed in the cliffs west of Eypesmoutli 

 (Thorncombe Beacon, Doghus and Down Cliffs), as recorded in 

 my previous paper,i will show how unlike the former is to the 

 latter. 



Thus the former is as much as 5| feet thick, whereas the latter 

 is about 2 feet, although it may amount to somewhat more 

 occasionallj". The former is mainly made up of a lithographic 

 stone with Grammoceras-striatulum types, derived examples of 

 Tetrarhyncliia thonicomhiensis, and derived lumps of this 

 Rhynclionella Bed. The latter shows sometimes about 2 inches 

 of the striatulum layer, while the T.-tliorncomhiensis Bed is, 

 according to my measurements, some 8 feet below the Junction - 

 Bed at Thorncombe Beacon : according to m}^ interpretation of 

 Day's measurements at Down Cliffs," it is more than 18 feet 

 below, about which something will be said later. 



Further, the Watton Bed shows no sign of Marlstone,'^ which is, 

 when present, a richl};^ fossiliferous horizon in the Western Cliffs ; 

 nor did I find any strata with the hifrons type of ammonite — • 

 only examples redeposited along with striatulum forms. 



In the Watton Bed there are certain peculiar Whitbian ammo- 

 nites — unfortunately in fragmentary condition, mainly only body- 

 chambers. Nothing of such forms has been noted for the Junc- 

 tion-Bed of the Western CJiffs ; but, of course, all the ammonite 

 fauna of that deposit has not been fully examined, for removal 

 of this matrix is very tedious. In the Watton Bed, however, 

 there were enough specimens to attract attention at once, and 

 3'"et I imagine that they are unusual for Whitbian deposits of the 

 South of England. About that it is inadvisable to speak too 

 positively as yet — first, because these ammonites require study; 

 and secondly, because the Whitbian ammonite fauna of the South 

 of England has been very imperfectly illustrated. These ammo- 

 nites have something of the appearance of certain small species 

 from the Jet-Bock of Yorkshire — at any rate, they suggest an 

 early date in Whitbian, about exaratiim, or even before tliat.^ 

 The Thecidellce, which are just below them, call to mind the 

 micro-brachiopod horizon below the Fish- and Insect-Beds of the 

 South-West of England. 



These matters will require further study later, see p. 400. 



] I, 5, p. 64. 2 ni, p. 285. 



•^ I, 5, p. 65. Later observations of a fallen block suggested some Marl- 

 stone matrix used up, but no fossils were found. Naturally, blocks may- 

 vary considerably in their constituents. 



■* Curiously enough, Mr. J. F. Jackson has found similar ammonites at a 

 higher horizon in the Watton Bed ; they are in a much better state of pre- 

 servation, and have a white matrix. 



