518 MK. S. S. BUCKMAN ON THE SO-CALLED 



30. On the so-called " Uppee-Lias Clay " of Down Cltpes *. 

 By S. S. BucKMAN, r.G.S. (Read May 14, 1890.) 



In a former paper t I gave a section of part of Down Cliffs, near 

 Seatown, Dorset ; but I had obtained no evidence of the palaeonto- 

 logical contents of the Bed 19. 



Partly, no doubt, on account of its position (only a little above 

 the Marlstone), and partly on account of its blue colour, this bed has 

 been called by Day J and by H. B. Woodward § " Upper-Lias Clay;" 

 and I think that I am correct in saying that this term has, in this 

 country, usually signified those argillaceous deposits which, occupying 

 a very similar position above the Marlstone, contain the fauna of the 

 Falciferum- and Commune-zones. 



Last summer I had an opportunity of further examining Down 

 Cliffs, and, after some search, was enabled to i)rocure sufficient 

 evidence to show what is really the correct horizon of the clay- or 

 marl-bed in question. The evidence consisted of Ammonites of the 

 genus Duonortieria ; but their condition was unsatisfactory for pre- 

 servation, since they were little else than impressions or casts in 

 the marl, and were often crushed. I was, however, able to preserve 

 a few specimens ; and, having frequently met with similar Ammo- 

 nites in the Cotteswolds, I was able to determine even those 

 specimens which I could not preserve. One species I could make 

 out with certainty, namely Bumortieria radians ||. Accompanying 

 this, was a wider-ribbed form of the same genus — a genus so easily 

 recognized by the peculiar straightness of the ribbing. The wider- 

 ribbed species was most probably Dumortieria Levesquei. 



ISTow, species of the genus Dumortieria are practically confined to 

 a limited horizon, namely, to strata to which I applied the terms 

 Moorei- and Dumortieria-heds ^, in other words, the base of the 

 Opalinum- and the top of the Jurense-zone ; and B. radians may be 

 regarded as a species distinctive of the top of the latter zone. In 

 that case, this blue marl is really only a part of the Yeovil Sands, 

 seeing that this species occurs also in them ; and this blue marl is 

 of distinctly later date than the blue clay of the White-Lackington 

 >Section **. Here, then, is a further instance of the later prevalence 

 of clayey conditions the further we go South. 



* This paper consists of notes supplementary to a paper on the Cotteswold, 

 Midford, and Yeovil Sands, &c., Quart. Journ. GeoL Soc. xlv. 1889, pp. 440- 

 473. 1- Ibid. p. 452. 



\ Day, " On the Middle and Upper Lias of the Dorsetshire Coast," op. cif. 

 vol. xix. 1863, p. 285. 



§ Geology of England and Wales, 2nd ed. p. 276. " The Upper Lias in 

 Dorsetshire is represented by a clay-deposit, which rests upon the re- 

 markable junction-bed " 



II In my former paper (p. 443) this species was alluded to as I), rkodanica. 

 I must refer the reader to the forthcoming Part Y. of my Monograph on 

 Ammonites (Pal. Soc. vol. for 1890) for the explanation of this matter. 



«[ Q, J. a. S. vol. xlv. p. 443. 



** Ibid. p. 450, bed " 2," &c. 



