Dr. M. C. Slopes — The Kentish Rag 'Dragon-tree'. 55 



It is obvious that a research of this nature may be indefinitely 

 extended ; but enough has been here set down to show that 

 Mr. Horwood may be justified in expecting some retention of 

 aragonite even in Jurassic strata. The change into calcite in stratified 

 deposits is really very slow. Aragonite shells are often affected by 

 solution in Cainozoic strata, but not ordinarily by conversion into 

 calcite. A study of compact Eocene limestones may be expected 

 to show calcite pseudomorphs, at any rate in some parts of the world ; 

 but European clays and sands alike seem to allow of the retention of 

 the aragonite state, until we reach well back into the Cretaceous 

 period. 



In the Gault of Folkestone we have a tendency for the development 

 of calcite. It would be interesting to know if this occurs in certain 

 zones, where percolation of water happens to be more free.' Certainly 

 the evidence of Jurassic limestones is strongly in favour of the general 

 change of aragonite into calcite in beds of this age, though aragonite 

 may exceptionally be preserved in certain argillaceous strata. We 

 can now hardly expect to find aragonite in shells older than the 

 Jurassic period. 



Sorby 1 held that aragonite shells often broke down into "fine- 

 grained calcite mud", and were thus lost sight of in limestones. 

 Rapid accumulation might, he thought, have saved them in some 

 Jurassic limestones ; but even then it is not clear that he regarded 

 the shells and corals thus preserved as still consisting of aragonite. 

 We ourselves find no evidence of the disappearance of aragonite shells 

 by granulization. Unless actually dissolved, they may remain as 

 aragonite, with their original forms and structures, though they have 

 come down to us from the opening of Cainozoic times. 



In view of the instability of aragonite as precipitated in certain 

 chemical experiments, it is interesting to find that the same 

 substance, when organically deposited, holds its own so well through 

 a long series of geological periods. 



II. — The 'Dragon-tree' of the Kentish Rag, with Remarks on 

 the Treatment of Imperfectly Petrified Woods. 



By M. C. Stopes, D.Sc, Ph.D., F.L.S., Lecturer in Fossil Botany, 

 Manchester University. 



FN the early numbers of the Geological Magazine the ' Dragon- 

 JL tree ' received considerable attention. It was thought to be 

 a Monocotyledon and described as a species of Draccena by Mackie in 

 1862 {Geologist, p. 401, pi. xxii). The specimen appears to have 

 attracted an unusual amount of interest prior to 1870, and it is 

 referred to by Mantell and other contemporary writers. Carruthers 

 placed it among the British fossil Pandanacese in 1868 (Geol. Mag., 

 p. 154). Like other specimens from the sandstones of the Iguanodon 

 Quarry (Lower Greensand of Maidstone), no internal structure 

 appeared to be preserved, and the determination of its nature rested 

 entirely on the external features. 



1 Quart. Journ. Geol. Soc, 1879. Proceedings, p. 83. 



