148 Geological Society : — 



teresting plant might easily be mistaken for portions of other and 

 very distinct plants, such as Karstenia, Halonia, Stigtneifia, Schizo- 

 pte'ris, Trickomanites, Fucoids, &c. The author describes two species 

 of Psilophyton, P. princeps and P. rohuslius. 



Dr. Dawson further described a new form of Lepidodendron (L. 

 Gaspianum) ; also some specimens of Coniferous wood related to the 

 Taa^us {Prototaxltes Logani), and some less clear forms belonging to 

 Knorria, Poacites, &c. The author also noticed the occurrence of 

 Entomostraca (Beyrichia), Spirorbis, occasional fish-remains, some 

 Brachiopods, and also rain-marks and ripple-marks in these Devonian 

 beds. 



2. " On some Points in Chemical Geology." By T. Sterry Hunt, 

 Esq., of the Geological Commission of Canada. (Communicated by 

 Prof. A. C. Ramsay, F.G.S.) 



§ I. Referring to his communications to other Societies in which 

 he had endeavoured to explain the theory of the transformation of 

 sedimentary deposits into crystalline rocks, and to the researches of 

 Daubree, Senarmont, and others, the author remarked, in the first 

 place, that the problem of the generation, from the sands, clays, and 

 earthy carbonates of sedimentary deposits, of the various siliceous 

 minerals which make up the crystalline rocks, may be now regarded 

 as solved ; and that we find the agent of the process to be water, 

 holding in solution alkaline carbonates and silicates, acting upon 

 the heated strata. Under some circumstances, however — such as 

 the presence of gypsum or magnesia — such anomalies might occur 

 as are presented by the comparatively unaltered condition of some 

 portions of the strata in metamorphic regions. 



§ II. Many crystalline rocks, formerly regarded as of plutonic 

 origin, are now found to be represented among altered sedimentary 

 strata ; and the chemical student in geology is now brought to the 

 conclusion that metamorphic rocks, such as granite, diorite, dolo- 

 mite, serpentine, and limestone, may, under certain conditions, 

 appear as intrusive rocks. This is chiefly owing to the pasty or 

 semi-fluid state which these rocks must have assumed at the time of 

 their displacement. 



§ III. The author next remarked that the hypotheses relating to 

 the origin of the two great groups of plutonic rocks — those with 

 potash and much silica, and those with soda and less silica — are not 

 satisfactory. 



§ IV. Mr. Hunt, considering that the water of the early palaeozoic 

 ocean difl'ered from that of the modern seas, in that it contained chlo- 

 rides of calcium and magnesium to a far greater extent, especially the 

 former, sulphates being present only in small amount, noticed that 

 the replacement of the chloride of calcium by common salt involved 

 the intervention of carbonate of soda and the formation of carbonate 

 of lime ; and that the continual decomposition of alkaliferous sili- 

 cates to form the vast masses of argillaceous sediments from the 

 felspathic minerals of the earth's crust, must have formed, and is 



