178 REPORT 1860. 



Arragonite*. Here then we have proof of a certain modicum of heat existing 

 in boiling-springs now extinct, which once pervaded these strata • for had the 

 heat of the water which left this deposit been much more, or less, than about 

 212° F., no such crystals could have been formed. Not far from the same 

 locality, in a thin seam of the cornbrash Oolite, I have found nodules en- 

 closing small Crustacea, the interior of which was filled with crystalline 

 blende. No other trace of zinc is to be seen in the country around t. The 

 same singular phenomenon may be observed in the neighbouring Lias-shale, 

 where the chambers of the Ammonites frequently contain blende\. This is 

 not a phenomenon peculiar to the district ; it illustrates the general con- 

 dition of the earth after these shells were deposited, and is best accounted 

 for by the vera causa of an elevated temperature ; it indicates that the fumes 

 of zinc, or one of its volatile combinations, must have penetrated the strata, 

 taking the form of blende in the chambers of the Ammonite, and having 

 been sealed up in these, escaped decomposition. 



The same account is applicable to the dissemination of carbonate and sul- 

 phide of lead and copper in the Permian and Triassic strata, and of the 

 particles of metallic copper in the mountain limestone; as well as to the de- 

 posits of calamine in the hollows of that rock, on the conditions of which de- 

 posits light is thrown by an experiment of Delanoue, who found that no pre- 

 cipitate of carbonate of zinc is produced by limestone at the common tempera- 

 ture, but that it is perfectly thrown down from a. warm solution of its salts. 



And here also it is worthy of remark, that in the experiments of Forch- 

 hammer to illustrate the formation of dolomitic strata, when a solution of 

 carbonate of lime was mixed with sea-water at a boiling heat, the compound 

 formed contained only 18 per cent, of carbonate of magnesia, but that the 

 proportion of magnesia increased with an increase of temperature; in the 

 experiments of Favre and Marignac, the composition of equal atoms, which 

 is that of many natural beds of magnesian limestone, was attained by raising 

 the heat to 392° F., and the pressure to 1.5 atmospheres; and in those of 

 Morlot a mixture of sulphate of magnesia and calcareous spar was com- 

 pletely converted, in the same circumstances, into a double salt of carbonate 

 of lime and magnesia, with sulphate of lime. 



The probable history of all the calcareous and magnesian strata, with 

 their interstratified cherts and flints, and interspersed chalcedonic fossils, is 

 that they are products of submarine solfataras, whence issued successively, 

 in basins variously extended, gases and springs capable of dissolving pre- 

 existent beds, which caused alternate depositions .of silica and carbonated 

 earths, and intermitting from time to time, allowed intervals for the succession 

 of organic and animated beings. 



The manner in which materials are furnished for extensive sedimentary 

 deposits by processes of disintegration dependent on subterraneous ema- 

 nations, has been observed by Bunsen in the solfataras of Iceland. He 

 describes the palagonitic rocks, formerly erupted there, as undergoing con- 



* Dr. Murray informs me that this Arragonite is found in a little bay within six miles of 

 Scarborough, in the seams and crevices of the upper calcareous grit. He describes it as 

 fibrous, compact, or imperfectly mammillated, wanting the oblique cleavage of calcite, 

 scratching Iceland spar, and flying into powder in the flame of a taper. Mr. Procter having 

 at my request taken the specific gravity of a fibrous specimen, finds it 3, and confirms Dr. 

 Murray's description of the other characters of this mineral. 



f The only peculiarity is that a basaltic dike traverses the district at a distance of a few 

 miles from the site of the fossils. 



J The Lias fossils sometimes also contain galena. Blum describes a bivalve from a fer- 

 ruginous oolitic rock near Semur, the shells of which consist entirely of crystalline lamina; 

 of specular iron ; and a cardinia from the lower lias, according to Bischof, likewise consists 

 of the same mineral, which we know elsewhere as a result of volcanic action. 





