298 



FOSSIL FOREST IN LULWORTH COVE. 



[Ch. XX. 



The thin layers of calcareous slate (%. 342) were evidently deposited 

 tranquilly, and would have been horizontal but for the protrusion of the 

 stumps of the trees, around the top of each of which they form hemispher- 

 ical concretions. 



The dirt-bed is by no means confined to the island of Portland, where 

 it has been most carefully studied, but is seen in the same relative position 

 in the cliffs east of Lulworth Cove, in Dorsetshire, where, as the strata 

 have been disturbed, and are now inclined at an angle of 45°, the stumps 

 of the trees are also inclined at the same angle in an opposite direction — ■ 

 a beautiful illustration of a change in the position of beds originally hori- 

 zontal (see fig. 343). Traces of the dirt-bed have also been observed by 



Fiff. 843. 



freshwater calcareous slate, 

 dirt-bed, -with stools of trees. 



freshwater. 



Portland stone, marine. 



Section in cliff east of Lulworth Cove. (Buckland and De la Beche.) 



Mr. Fisher, at Ridgway; by Dr. Buckland, about two miles north of 

 Thame, in Oxfordshire ; and by Dr. Fitton, in the chffs in the Boulonnois, 

 on the French coast ; but, as might be expected, this freshwater deposit 

 is of limited extent when compared to most marine formations. 



From the facts above described, we may infer, first, that those beds of 

 the upper Oolite, called " the Portland," which are full of marine shells, 

 were overspread with fluviatile mud, which became dry land, and cov- 

 ered by a forest, throughout a portion of the space now occupied by the 

 south of England, the climate being such as to admit the growth of the 

 Zamia and Cycas. 2dly. This land at length sank down and was sub- 

 merged with its forests beneath a body of freshwater, from which sedi- 

 ment was thrown down enveloping fluviatile shells. 3dly. The regular 

 and uniform preservation of this thin bed of black earth over a distance 

 of many miles, shows that the change from dry land to the state of a 

 freshwater lake or estuary, was not accompanied by any violent denuda- 

 tion, or rush of water, since the loose black earth, together with the trees 

 which lay prostrate on its surface, must inevitably have been swept away 

 had any such violent catastrophe taken place. 



The dirt-bed has been described above in its most simple form, but 

 in some sections the appearances are more complicated. The forest of 

 the dirt-bed was not everywhere the first vegetation which grew in this 

 region. Two other beds of carbonaceous clay, one of them containing 

 Cycadece^ in an upright position, have been found below it, and one 



