in the MetUtcrrnnean. 53 



by means of substances dissolved in waters, ivhcre they arc found in 

 a gelatinous state. 



II. Facts which prove that Petrifactions are now forming in the 

 bosom of existing seas, analogous to those of Geological times. 



The shells in the bottom of the Mediterranean, abandoned by the 

 animals which formed them, there meet with the conditions indica- 

 ted above as indispensable to their petrifiiction. They are sunk in 

 considerable masses of water, holding notable quantities of carbonate 

 of lime in solution. Accordingly, to the calcareous carbonate which 

 composed the shell in a fresh state, a new quantity may be added or 

 substituted, furnished by the waters of the sea, and which replaces 

 the animal matter, and the carbonate of the original lime. This is 

 just what wo observe, and in different degrees, according as the 

 petrifaction is more or less advanced. We shall afterwards study, 

 with the necessary details, the whole of the different degrees of this 

 phenomenon. Let us now confine ourselves to the simple announce- 

 ment of the fact, which we shall immediately examine in such a way 

 as to remove all doubts. 



But it is not on our own coasts only that we find shells brought 

 to a state of petrifaction in our own era ; we have received from 

 Algiers masses of shells transformed into a crystalline limestone of 

 a peculiar whiteness and ])rilliar.cy, similar to alabaster. We find 

 in these shell-rocks, as they may be called, small rolled pebbles, en- 

 crusted with a stalagmitic and crystalline coating. This same 

 coating appears to be the cement which has agglutinated the rolled 

 pebbles ; the latter are siliceous or calcareous. Among the shells 

 composing these masses, we notice only genera and species of our 

 own epoch, particularly Pcctunculus and Cardium ; more rarely uni- 

 valves. The ofttccrs who have brought us these shell petrifactions 

 from the neighbourhood of Algiers, assure us that they are formed in 

 our own times, and in the historical epoch. But as we have not our- 

 selves observed these masses of shells in the places where they occur, 

 we cannot very positively assert that such is really their origin. 



We may add, that it is not shells alone which may be thus 

 brought to the state of petrifaction in the midst of salt waters. It 

 is easy to produce examples of vegetable petrifactions formed in 

 recent times. We may first refer to the curious observation of M. 

 Lyell. This geologist found grains of chara petrifying, in the pre- 

 sent day, into calcareous matter in the lakes of Scotland, just as 

 seeds of tlio same vegetable petrified into calcareous matter in the 

 lacustrine waters of the old world. Captain Baux observed a fact of 

 the same kind in tlie island of Moiiador. Stalks of fucus, belonfjine: to 

 the same species as those living in the surrounding sea, have become, 

 as it were, centres of attraction for the calcareous and siliceous salts. 

 'J'hesc substances have precipitated themselves on tho stalks, around 

 which they are moulded. Some of these stalks, as yet incompletely 



