214 Dr. FiTTON on the Strata below the Chalk. 



whole of this series, including both the bituminous strata of Kimmeridge, 

 and the more complex group beneath, is fully developed in the Lower Bou- 

 lonnois, of which I have given an account in another paper read before this 

 Society*; and that the coast of Yorkshire near Scarborough is composed of 

 similar strata f. 



(108.) On a general view from the heights in Purbeck or Portland, of the 

 great bay or excavation of the coast, of which the Isle of Purbeck forms the 

 east wing, and that of Portland the western promontory, it is natural to 

 suppose that the strata in both places are the remaining portions of a wide 

 plane, which at one time passed continuously through both places, and formed 

 the reflected portion of that which rises from beneath the chalk and runs 

 in a nearly uniform direction from Ballard Hill to the heights near Lulworth 

 Cove. This ridge, if continued, would pass through Weymouth : but the 

 chalk is suddenly interrupted at Whitenore Cliff, and its main outcrop on the 

 west of that place, being directed towards a point about 15° or 16° north of 

 west, makes an angle of about 20° with its previous range through the Isle 

 of Purbeck. On a close examination, this change is found to be attended 

 with some very remarkable circumstances ; the coast on the north and west 

 of Whitenore having been the scene of great disturbance, by which a very 

 complex series of faults has been produced. The general disposition of 

 the strata, however, is still that of a saddle ; the northern side of which dips 

 to the east of north, while the beds in the Isle of Portland, (the only re- 

 maining portion of the slope on the south side,) decline towards a point about 

 48° east of south;};. The upper beds of Portland are therefore but a part 

 of the mantle-shaped covering which once enveloped the lower strata both 

 in Portland and in the intermediate space from thence to Kimmeridge Bay, 

 where indications of the mantle-shaped arrangement are still visible ; the 

 strata on the east of the bay sinking into the sea between Tillywhim and 

 Durlstone Head, very much in the same manner as they do at the Bill of 



and Mr. De la Beche, so often referred to in the text, has been printed in the beginning of the 

 present voUinie of the Geological Transactions. 



* Proceedings, vol. i. p. 6. 



t Sedgwick; Ann. of Phil. 1826. J.Phillips; Geology of Yorkshire, 4to, 1829. 



J The strike in Portland is well determined by the position of the two points on the opposite 

 side of the island, where the beds beneath the stone rise from the sea. These are, — on the west 

 coast, a spot almost due west of the words " H"^. Light " in the Ordnance Map ; and, on the east 

 coast, the place where the shore is cut by a line passing through the letter c in " Church-hope," 

 and the bottom of the letter e in the word " isle ". The line joining these opposite points, 

 makes an angle of about 48° with the meridian ; the dip being consequently directed to about 48° 

 east of south. See the Map, Plate VIII. 



