10 INFERIOR OOLITE AMMONITES. 



of quite 30 feet, and we do not then find either the top or bottom of the zone. 

 It is almost unfossiliferous, but occasionally Cosmoceras Parhinsoni, Perisplbinctes 

 Martinsii, and some Brachiopods are found. The most fossiliferous exposure of 

 the Parkinsoni-zone, as far as Ammonites are concerned is at Halfway House, 

 where the fossils occur in the lower portion, and at Broad Windsor, and Burton 

 Bradstock, Dorset, and Crewkerne Station, Somerset. The deepest development 

 of the Humphriesianum-zone with which I am acquainted is at Oborne, where it is 

 divided into two distinct beds with distinct Faunoe, measuring 5 feet altogether. 

 The. upper portion contains Cosmoceras subfurcatum (Schloth.) = Am. niortensis, 

 d'Orb., Cosm. Garantianum (d'Orb.), Perisph. Davidsoni, S. Buck., &c. Below the 

 Humphriesianum-zone proper comes the Sauzei bed, which may probably after all 

 be only a subzone of the Humphriesianum. It is G inches thick at Oborne. The 

 greatest development of the Sowerbyi-zone is at Halfway House, where it is about 

 4 feet, and contains a large number of species of the genus Harpoceras. We have 

 lastly the Murchisonas-zone, which attains as much as 4 — 5 feet at Corton Downs in 

 Somerset. 1 Therefore we have, putting these maxima developments of the Inferior 

 Oolite all together, a thickness of not much less than 50 feet. Were we able to 

 see a complete opening near Sherborne we should expect the beds there to be 

 best developed in every way ; while, as they extend westwards, they gradually 

 thin out until at Stoford they are only about 6 feet thick ; and at Bast Coker, 

 because some are absent they are not more than 3 — 4 feet. We do not know, 

 however, how much of the upper part of the Parkinsoni-zone, there represented, 

 may have been denuded. 



Paleontology. 



Before commencing any description of the various species we must consider 

 their classification. The genus " Ammonites " having become unwieldy, and not 

 being in accordance with the usages of modern science, we find that a large number 

 of new genera have been proposed, with the intention of taking its place. The 

 late Dr. Wright in his 'Monograph on the Lias Ammonites,' devoted a consider- 

 able amount of space to a very full and excellent description of all the systems of 

 classification that had been proposed. In fact he gives us an account of the 

 classification, not only of the Ammonites, but of the Cephalopods in general. 

 With the Ammonites he commences with the first efforts at subdivision, viz. L. von 

 Buch's, into families, continuing with Prof. Quenstedt's additions, a whole resume 

 of d'Orbigny's twenty-one sections, and ending with a complete account of the 



1 The Opalinum-zone is shown near Broad Windsor and at Burton Bradstock, Dorset, and near 

 Haselbury, Somerset, and the amount exposed varies from 2 — 5 feet in thickness. Lioceras opalinum, 

 and Terebratula infra-oolitliica are the typical fossils. 



