32 GASTEROPODA OF THE INFERIOR OOLITE. 



Gasteropoda on this line to entitle it to the dignity of an " Univalve Bed." The 

 fossils are mainly those characteristic of the Lower Division, and more especially 

 of the Murchisona-zone ; e.g. Cirrus, usually a fossil of a low horizon. The other 

 Gasteropoda from here will be named in their due places. The upper portion 

 of this in all probability shades off into the concavus-heds, or so-called Sowerbyi-zone, 

 but as there are no special traces of Gasteropoda here we need not go further into 

 the inquiry. There are signs of the so-called " Sowerbyi "-zone in a quarry 

 on the north side of the Bredy, but I found no Gasteropoda there of any conse- 

 quence. 



Again, the line between the Lower and Upper Divisions of the Inferior Oolite 

 cannot be laid down to an inch or two with absolute certainty in the cliff section. 

 This doubt arises mainly from the feeble and imperfect development of the 

 Humphries! anus-zone, a failure very characteristic of South Dorsetshire. As far 

 as an inspection of this section goes there seems to be no independent development 

 of the Humphries ianus-zone at all otherwise than as an adjunct to the rich-shell at 

 the base of the Parkinsoni-zone (PJ. This was noticed by Oppel, who, whilst 

 alluding to the trifling thickness of the Inferior Oolite, speaks of the fossils of the 

 Humphriesianus- and Parkinsoni-zcmea being found together in one and the same 

 bed of Oolite. To a certain extent this is so, and if such a zonalist as Oppel 

 admitted the fact the evidence in its favour must be very strong indeed. 



We have then to consider the character of the shell-bed which I have distin- 

 guished as Pp It is mainly situated towards the lower portion of the third block 

 of limestone, and is by far the most important shell-bed in the Burton Bradstock 

 Cliff. A portion of it also belongs to the next block, the split taking place through 

 the midst. The result is that when the larger blocks break up there is a double 

 surface presented to the collector's chisel. Astarte obliqua is very abundant, and 

 there are also other species of Astarte, so that this is sometimes known as the 

 Astarte-bed. The upper part of P : is crowded with T. sphaeroidalis, whilst in 

 the lower part the Astarte is most abundant. It is in this lower part that the 

 Gasteropoda of this shell-bed principally occur. Specimens of moderate-sized 

 Am. Parhinsoni are by no means uncommon in the Astarte division of P l5 and may 

 be found quite down to the base of the shell-bed. Sometimes, however, in the 

 very base of the bed, and in that portion which belongs to the lower block, fair- 

 sized specimens of Am. Humphriesianus, or a very closely allied Stephanoceras, may 

 be found. It is just possible that there may be a slight unconformity between the 

 two lines so that, here and there, specimens belonging to an older and lower zone 

 are sometimes adherent to the main mass. In this way an uncompromising 

 zonalist might seek to explain the apparent admixture. However that may be, it 

 is perfectly certain that specimens of Am. Parhinsoni are to be found quite as low 

 as any of the Gasteropoda hereafter to be described, and therefore I have no hesi- 



