324? Geological Society. 



mentioned some years ago by Mr. Webster*. Since that time Dr. 

 Buckland and Mr. De la Beche have inferred that both these trunks 

 and the Cycadeae described by the former f as occurring in the same 

 stratum, must actually have grown in the places where their remains 

 are found \ > an d, more recently, Professor Henslow has ascertained 

 the existence of two other beds of clay, between that which includes 

 the trees and Cycadeae and the Portland stone. The author of the 

 present notice was so fortunate as to visit the island, during the last 

 summer, at a moment when the remains of Cycadeae were found in 

 one of these loner beds, and to see some of them before they were 

 disturbed. The bed in which they occur is between those which are 

 called by the quarry-men "Cap" and "Skull-cap", both of which 

 consist of freshwater limestone j the latter being separated from the 

 Portland stone by no more than two or three inches of clay. The 

 Cycadeae in this lower bed were in some cases of very large horizontal 

 dimensions, and, like those in the dirt above the "Cap", were in 

 the upright position, and apparently in the places where they ori- 

 ginally grew. 



The author found thin beds of clay, with more or less admixture 

 of mechanically divided matter, alternating in several other instances 

 with the fissile limestone at the lower part of the Purbeck forma- 

 tion. Even the " Cap", which in Portland is generally a continuous 

 mass of limestone six to eight feet thick, without stratification, in- 

 cludes, in other places at its lower part, alternations of thin strata of 

 clay. 



The "Cap" is for the greater part compact ; but it includes ca- 

 vities lined with botryoidal carbonate of lime, and in other respects 

 resembles very strongly the travertine of Italy. In the clay or dirt 

 beneath it, no trees are found along with the Cycadeae, in the Isle of 

 Portland ; but the author observed near Poxwell, on the north-east 

 of Weymouth, part of a silicified trunk, in a bed of " dirt", which he 

 thinks may, not improbably, be inferior to the "Cap", and, conse 

 quently, the same with the lower of the two beds which in Portland 

 afford the Cycadeae. 



The author ascertained, on attentive examination, that casts of one 

 or more species of Cypris exist throughout the whole series of the 

 slaty limestone beds above the Portland stone : the boundary of the 

 two formations being, as Mr. Webster had supposed, immediately 

 below the "Skull-cap": and, generally, the portion of the Purbeck 

 formation which adjoins that of Portland, may be said to consist of 

 freshwater limestone, alternating with thin beds of clay and mecha- 

 nically worn matter; — two of which beds, at least, contain the re- 

 mains of plants standing in the places where they grew : the whole 

 reposing upon strata which abound remarkably in marine shells. 



The top of the Portland series, in which these shells are so abun- 

 dant, has many points of resemblance to the recent agglomerated 



• Geological Transactions, Second Series, vol. ii. p. 42. 



f Ibid. p. 395. X Geological Proceedings, vol. i. p. 2 ID. 



