THE PETRIFIED FOREST. 399 



but Dr. Fitton mentions the occurrence of casts 

 of Cyprides. These strata are covered by the 

 modern vegetable soil, which but little exceeds 

 in depth the ancient one above described, and 

 instead of supporting cycadeous plants, and pine- 

 forests, barely maintains a scanty vegetation, 

 there being scarcely a tree or shrub on the whole 

 Island. 



There is a seam of black eaf'th at the distance 

 of five feet, and another two feet lower, beneath 

 the dirt-bed, indicating two short intervals during 

 which vegetable matter had begun to accumulate 

 on the surface of the uppermost beds of Portland 

 stone, when they were first emerging above the 

 level of the sea. In these layers Dr. Fitton 

 observed remains of cycadeous plants.* 



The dirt-bed extends through the north of 

 Portland, and appears, as we have seen, on the 

 coast of the peninsula of Purbeck. It has been 

 discovered by Dr. Buckland near Thame, in Ox- 

 fordshire, and by Dr. Fitton, in the vale of 

 Wardour. It also occurs at Swindon, Wilts, 

 where fossil coniferous wood abounds, and some 

 specimens of cycadeas have been obtained; and 



* See Wonders of Geology, vol. i. p. 362. For a detailed account of the 

 Portland quarries, and the phenomena concisely described in the text, consult 

 Dr.Fitton's " Memoir;" and Dr. Buckland and Sir H. De la Beche, "On the 

 Geology of Weymouth," Geol. Trans, vol. iv. second series. 



