24 GASTEROPODA OP THE INFERIOR OOLITE. 



by the predominance of certain facies, and this peculiarity gradually loses its dis- 

 tinctive character, and frequently the beds their f ossiliferous wealth, as the confines 

 of the adjoining area are approached. Hence I do not feel called upon to indicate 

 the boundaries too absolutely, as if one were defining the limits of a parish or a 

 polling district, though something of the sort may be attempted in giving the 

 details of the four great districts. As regards the name of the second district it 

 certainly includes more, both to the north and to the south, than the actual 

 Cotteswold Hills. Hence our second district is not precisely coterminous with the 

 Inferior Oolite of the Cottes wolds. Moreover, there is another difficulty in this 

 connection, viz. where to locate the very exceptional development at Dundry. 

 Both the facies and lithology of those fossiliferous beds recall some of the most 

 typical of the Dorsetshire sections, in spite of their lying well to the north of the 

 Mendips. But on the other hand the large development of coral in the Parhinsoni- 

 zone quite distinguishes this remarkable outlier, which topographically must be 

 included within the second district, unless we are to regard it as sufficiently 

 important to constitute a region by itself. 



Now, the Dorset district possesses an essentially Cephalopod facies in the main 

 with, as we have already seen, a thin development of sediment. These conditions 

 seem to have been eminently favorable to the growth of Gasteropoda, and the 

 subsequent mineral changes have also been favorable to their preservation as fossils. 

 Hence it is to the collections from these beds that we must look, not only for the 

 greatest number of species, but also for the best preserved specimens on which we 

 must depend for the illustration of this Memoir. In fact, if all the available 

 Gasteropods of the Inferior Oolite were as well preserved as are those from the best 

 localities in Dorsetshire, the task I have undertaken would prove a much easier one 

 than is likely to be the case. The essentially Cephalopod character of the 

 facies is maintained as regards the Lower Division, even into South Somerset, 1 but 

 the Upper Division, or equivalent of the Cotteswold Ragstones, already begins to 

 fail in Ammonites ; though the shell-beds swarm with Brachiopoda and Trigonia 

 together with a moderate supply of the Gasteropoda peculiar to the Upper Division. 



In the Cotteswold district the deposits are so bulky that it would be difficult to 

 name any one facies as markedly predominant. The three thin " coral reefs," if 

 indeed they are worthy of such a grandiose name, mark the more classical portion of 

 the district which extends from the neighbourhood of Stroud to the neighbourhood 

 of Cheltenham. Hence the facies is partly coralline ; but there are also examples 

 of the brachiopod and echinoderm facies in abundance. Ammonites are compara- 

 tively rare, and, as far as I can ascertain, above the Cephalopoda-bed (zone of 

 Am. radians), of very few species. The Lower Division is better supplied with 

 Gasteropoda than the Upper Division, or Ragstones, but these shells cannot be said 

 1 The axis of the Mendips is taken as the division hetween North and South Somerset. 



