GEOLOGY. 249 



nearly resembled, among terrestrial rocks, by consolidated volcanic 

 ashes. Is there anything in this fact of aggregation which touches the 

 nebular hypothesis ? 



PRODUCTION OF CRYSTALLINE LIMESTONES. 



In the Annual Sci. Dis. 1862, p. 289, an account is given of experi- 

 ments made by Rose of Berlin, tending to show that chalk or compact 

 limestone cannot be converted into crystalline limestone (or calc spar) 

 by exposure to high temperature in close vessels ; and that the experi- 

 - ments made some years since by Sir James Hall, tending to prove the 

 affirmative of the proposition, were eroneous. Recently, however, 

 Rose has repeated his investigations on the subject, and has now ob- 

 tained results which differ entirely from those he formerly published, 

 and which fully confirms the correctness of Sir James Hall's conclu- 

 sion, that marble can be produced by exposing massive carbonate of 

 lime to a high temperature under great pressure. The experiments 

 were made with aragonite from Bilin, in Bohemia, and with litho- 

 graphic limestone. In one case, the mineral was heated in a wrought- 

 iron cylinder, and in the other, in a porcelain bottle, special precau- 

 tions being taken to exclude the air, and make the vessels as near air- 

 tight as possible. These were exposed to a white heat for half an 

 hour, and, on cooling, both the aragonite and the lithographic lime- 

 stone were found to be converted into crystalline limestone, the former 

 very much resembling Carrara marble, and the latter a grayish-white 

 granular limestone. The change took place without any material 

 decomposition, the resulting marble containing a trifle less carbonic 

 acid than the lithographic limestone from whicli it was produced. 

 Silliman's Journal. 



THE FLORA OF THE DEVONIAN PERIOD. 



Prof. Dawson, of Montreal, communicates to the Journal of the Geo- 

 logical Society (London), the following general conclusion arrived at 

 by him, from a careful study of the " Flora of the Devonian Period in 

 North Eastern America." 1st. In its general character, the Devonian 

 Flora resembles that of the Carboniferous Period, in the prevalence of 

 Gymnosperms and Cryptogams ; and, with few exceptions, the generic 

 types of the two periods are the same. Some genera are, however, 

 relatively much better represented in the Devonian than in the Car- 

 boniferous deposits, and several Carboniferous genera are wanting in 

 the Devonian. 



2d. Some species, which appear early in the Devonian Period, con- 

 tinue to its close without entering the Carboniferous ; and the great 

 majority of the species, even of the Upper Devonian, do not reappear 

 in the Carboniferous Period ; but a few species extend from the Upper 

 Devonian into the Lower Carboniferous, and thus establish a real pas- 

 sage from the earlier to the later Flora. The connection thus estab- 

 lished between the Upper Devonian and the Lower Carboniferous is 

 much less intimate than that which subsists between the latter and the 

 true Coal-measures. Another way of stating this is, that there is a 

 constant gain in number of genera and species from the Lower to the 

 Upper Devonian, but that at the close of the Devonian many species 

 and some genera disappear. In the Lower Carboniferous, the Flora is 



