Dr. FiTTON on the Strata below the Chalk. 213 



about 300 feet of the bituminous Kimmeridge clay are disclosed on the coast of Purbeck; 

 which probably, is not far from the total thickness of the formation. 



The beds here consist in general of bituminous fissile clay in a large jiroportion, alternating 

 with thin courses of brown subcalcareous stone, or bituminous limestone. The clay in some 

 cases contains so much bituminous matter, as to be used for fuel under the name of " coal * " ; in 

 others it contains a large proportion of carbonate of lime, alternating with the laminae of the clay. 

 To these more calcareous and whiter beds the name of "White Lias" is given in the neigh- 

 bourhood. 



The connexion of the Kimmeridge clay with the Portland sand and stone is visible, though the 

 section is in some points inaccessible, at a place between Gad Cliff and the commencement of the 

 lower cliffs of the bay, where the following was the order : — 



1. Dark sandy marl (Portland sand) about 100 feet. A specimen taken hei'e about 100 feet 

 below the Portland stone, consists of light grey, soft, calcareous matter, including minute green 

 particles in very large proportion; the whole very much resembling some portions of the 

 Upper, and of the middle strata of the Lower green-sand. 



2. A series of beds about 30 feet in thickness, composed of shale, in part so bituminous as to 

 serve the purposes of fuel; in other places passing into a very bituminous soft fissile limestone 

 (" White lias ") of a light brown or grey colour, which on decomposing becomes almost white. 

 The dark surfaces of the fissile beds are spotted with numerous light grey specks, probably the 

 remains of organized bodies. 



Another form in which calcareous stone alternates with the bituminous shale above mentioned, 

 is that of a dark brown stone, — sometimes of the consistence of indurated marl, effervescing 

 freely, sometimes acquiring a flat conchoidal fracture and greater hardness, and but slightly 

 effervescent. 



The strata around Kimmeridge Bay, which seem to belong to a lower part of the series than 

 the second group above mentioned, include a remarkable bed of brown, bituminous, and some- 

 what gritty limestone, about tw(j feet thick, which is divisible into rhomboidal fragments. This 

 is succeeded by a considerable thickness of shale, less bituminous than the " coal " ; which in- 

 cludes with other fossils, great numbers of Ammonites biplex much compressed, and alternates witli 

 thin beds of the limestone. At Hen Cliff three or four such beds occur in the shale. One of the 

 same character is conspicuous in the arch or curve of the cliff at Kimmeridge Bay, and another 

 about 30 feet below, seems to be the lowest stratum of the Isle of Purbeck. 



The Kimmeridge clay^ sinks into the sea at Gad CHff, and does not again 

 appear till after an interval of seven or eight miles^ where a very good sec- 

 tion is visible in Ringstead Bay on the west of Whitenore. The beds which 

 occupy the shore thence to Weymouth Bay form the transition from this 

 clay into the Oxford oolite ; and as a full account of them will be given by 

 Dr. Buckland and Mr. De la Bechef, I shall only mention here that the 



* It burns with a bright flame, emitting a very disagreeable smell, and leaves a grey, light, and 

 spongy cinder. 



t The country around Weymouth had been previously illustrated by a paper of Professor 

 Sedgwick, in the Annals of Philosophy for 1826, vol. xi. p. 339, &c. ; where its resemblance to 

 the cliffs near Scarborough was pointed out, and the relations of the beds between the Port- 

 land strata and the Oxford oolite, in different places, explained. The Memoir of Dr. Buckland 



