54 Observations on the Petrifaction of Shells 



petrified, shew some traces of vegetable tissue. M. Baux could 

 compare them with the fuci of the neighbouring sea, and he found 

 that the petrified fuci were identical witli Fucus natans. 



M. Blast, of Bombay,* has discovered, in the neighbourhood of 

 Cairo, an entire forest converted into silex ; the vessels, medullary 

 rays, and even the most slender fibres, are distinctly visible. The 

 petrified trees are from 16 to 18 metres in length. This phenome- 

 non extends over a surface of many hundred miles. The whole de- 

 sert which is crossed by the road from Cairo to Suez is strewed with 

 these ti'ees, which seem to have been petrified on the spot, and in 

 the existing era. At least this forest is covered by nothing more 

 than sand and gravels. The latter, and the trees embedded in 

 them, rest on calcareous limestones, which contain oysters with 

 their texture and colour so little altered, that one would believe that 

 they had been but recently left by the waters of the sea. It is 

 therefore probable that these substances belong to our own era ; and 

 we may adduce this interesting fact as tending to prove the trans- 

 formation of living shells into new calcareous carbonate.f 



We may add, in the last place, that the waters of the sea are not 

 the only ones which can cause the petrifaction of shells in the exist- 

 ing period. In India, in the territory of Kurneel, there is a ther- 

 mal spring which forms abundant calcareous deposits, and in which 

 numerous freshwater shells of the genera Melania andPlanorbis are 

 found. These shells, in different states of petrifaction, are some- 

 times entirely converted into calcareous spar, while others preserve 

 only their interior mould ; and, lastly, there are some of them 

 covered with quartz crystals, while in others these ciystaUizations are 

 in a rudimentary state. The shell deposites formed by the thermal 

 spring of Kurneel, have a consistency analogous to that of the sili- 

 ceous tufas of the warm springs of the Geysers in Iceland. The 

 transformation of the shells of living Melania and Planorbis into 

 siliceous matter is a much more surpi-ising fact than the conversion 

 of the shells of the Mediterranean into calcareous matter different 

 from that of which they were primitively constituted. 



The facts which we have passed in review sufficiently demonstrate, 

 in our opinion, the reality of the phenomenon of the petrifaction of 

 shells in the present day, and impart to it besides a remai-kably 

 general character. We must now examine the phenomenon more 

 closely, by following the progress, and pointing out the differences 

 which present themselves according to the diversity of the species. 



* L'Institut, April 1846, p. 116. 



t Along with these facts, which we are unable to give on our own autho- 

 rity, we may add the two following, which are of great value in reference to 

 the question now before us : — 



The Oardium edulc, in a petrified state, 'if said to form considerable banks at 

 the mouth of the Somme. 



At Caucale, oyster-shells, which have been thrown into the sea after having 

 appeared at table, there become petrified like our shells in the Jlediterranean. 

 If this statement be correct, it is evident that it meets all ol>jectious. 



