PORTLAND EOCKS OE ENGLAND. 193 



No. 11 consists of about 26 feet of very curious material : it is a 

 liver-coloured mixture of marl and sand, with isolated nodules and 

 thick continuous bands of a sandy cement-stone. The fossils in 

 these cement-stones are not numerous, but they are useful ones. We 

 find here Mytilus autissiodorensis, vrhich occupies the same horizon, 

 both elsewhere in England and at Boulogne, with Pecten solidus, 

 Cyprina implicata (as at Boulogne), Cyprina elongata^ an Isocardia, 

 and Ammonites Boisdini(^.) and A. bij.dex. 



No. 12 is a perfect lumachelle of small oysters, the Exogyra 

 hnmtrutana. These exclude all other shells, and by themselves 

 form the mass of the rock with a marly infilling. It is 7 feet thick. 



No. 13 consists of 10 feet of yellow sandy beds with hardened 

 bands clearly marked off form the bluer beds below. They contain 

 but few fossils beyond Cyprina implicata and an Area. 



No. 14 is a mass of sandy marl, gradually changing into true 

 Kimmeridge Clay, the probable junction being inaccessible or covered. 

 More of this can be seen on the western side than beneath Yerne 

 Fort, where all the other members are better observed. At least 

 30 feet are exposed for examination ; but there may be much more. 

 They are speckled blue and yellow, and have many small-sized 

 doggers towards the upper part, but larger ones below. A good 

 series of fossils might be collected from this mass ; those I have 

 noted are of great value for correlation; they are: — the true Am- 

 monites hiplex : an ornamented new species of Natica^ which I call 

 incisa ; Lima holoniensis, which marks a special horizon at Boulogne; 

 Pecten Morini and Avicula octavia, very characteristic forms ; Tn- 

 gonicB incurva, muricata, Pellati, and a new undulate species 

 ("though there is a total absence of T. gibhosa) ; also two new Bra- 

 chiopoda (the first hitherto recorded from British Portland rocks), 

 RJiynclioneUa portlandica and Piscina Hump>}iresiana. Pleuromya 

 tellina also occurs, occupying the vertical position. 



In all this series (Nos. 10-14), which constitutes the "Port- 

 land Sand," I have not seen any glauconite, nor are there any 

 pebbles to my knowledge ; but a gradual change is demonstrated 

 — undisturbed by local variations, and only exhibiting the distur- 

 bances elsewhere by slight alterations in the character of the de- 

 posits. The fauna, though connected with that of tlie Portland 

 Stone, is more allied to that of the upper part of the Kimmeridge 

 Clay — a fact of which, in my opinion, the French geologists make 

 an inverted use. 



2. St. Allan's Head and Kimmeridge (fig. 2, PI. YIII.). 



A comparison of the above typical section, derived from both 

 the east and west sides of the isle (between which, in the lower 

 parts, there is little difference), with the development twenty miles 

 to the east, will give an idea of the rapidity with which changes 

 are taking place. 



The great quarries on the coast to the south of Worth Maltravers 

 give admirable sections of the upper beds. The botryoidal Purbeck 

 limestone and underlying shale are at once recognized ; and then 



