LOWER GREENSAND. 3 



I. The Perna beds, which here form the base of the Lower Greensand, rest upon 

 Weald clay ; the junction between the lacustrine series of the latter with the marine 

 deposits of the former exhibit no trace of disturbance; a thin seam of bone-bed, composed 

 of the teeth of fish of lacustrine species, attest a change of conditions similar to that 

 observed in some junction-beds in other formations, as between the Upper Keuper and the 

 Lias, and the Upper Silurian and Devonian series. This junction, which is only sometimes 

 visible, occupies about eight inches of vertical thickness ; on one occasion I succeeded 

 in detaching a block of rock, about a foot thick, from the beds, the lower half of 

 which contained the lacustrine shells of the Weald clay, whilst in the upper half Perna 

 Mulleti, Desh., Exoyyra sinuata, Sow., and other Lower Greensand shells, were found. 

 The Perna beds rise from the base of the cliff, at a point a few yards to the east of the 

 flag-staff of the coastguard-station ; they consist of dark-blue sandy clay and greenish 

 sand, forming in parts a very hard rock, and characterized by that remarkable shell Perna 

 Mulleti, Desh., which is not found in any other bed in the section. Nearly one hundred 

 species of marine shells are found in the Perna beds ; among these Nautilus Requinianus, 

 d'Orb., and Exoyyra sinuata, Sow., appear for the first time, of very large size, and 

 Hemipneustes Fittonii, Porb., among the Echinida, with the remains of fish belonging to 

 the genera Lamna, Odontaspis, Saurocephalus, Hybodus, &c. 



II. The Atherfield Clay is of a drab colour, passing into bluish-gray, and contains 

 flat nodular masses. Ammonites Deshayesii, Leym., Pinna Robinaldina, d'Orb., and several 

 other species of Conchifera, with the bones of a Turtle, and the remains of Echinidae, are 

 found in this bed. 



III. The Crackers, so called from the noise produced by the waves dashing over the 

 ledges formed by these rocks on the shore, are the most interesting fossiliferous group of 

 the entire series, and consist of alternations of sandy clays and clays, and two layers of 

 ferruginous sandy nodules. All the clays resemble Pullers' earth, and the sand between 

 the nodular concretions in the lower bed is sometimes indurated into an imperfect stone. 

 The lower part of this group is a brown clay and sand, called the Lower Lobster bed, from 

 the number of Astacus Vectensis, Bell, found therein ; the succeeding beds are sands, 

 containing concretionary masses of sandstone full of beautiful fossil shells, Ammonites 

 Deshayesii, Leym., Pholadomya Martini, Porb., Myacites plicata, Sow., Corbula striatula, 

 Sow., and several other Conchifera. Many of the Myada are found in the upright position 

 they assumed during life. The lower sandstone, from a foot to eighteen inches in thick- 

 ness, is almost entirely made up of Gervillia aviculoides, Sow., Trigonia Dadalaa, Park., 

 Ammonites Deshayesii, Leym., and other shells. The upper layer of sandstone contains 

 coniferous wood and a Teredo, and the upper clays are fossiliferous throughout. In the 

 concretionary nodules of the lower series of this group I have collected Pseudodiadema 

 Autissodorense, Cott., P. Ibbetsoni, Forb., and Hemipneustes Fittoni, Porb., with the 



