A SKETCH OF GEOLOGY. l 



Xenophanes' theory. To-day, every person who has gained an insight into 

 palaeontology, knows that the fossils found in most of the sedimentary rocks 

 are originated by animal or vegetable remains, which, became imbedded in the 

 mud at the bottom of the sea, during former ages. In speaking of fossils, we 

 generally describe them as remains of animals and of plants, which is not 

 in accordance with the facts, at least not for the majority of them, inasmuch 

 as, in the larger number, not a particle of organic matter is preserved, and 

 only the form of the imbedded body retained. The original animal or vege- 

 table substances dissolved and became replaced by calcareous, siliceous and 

 other minerals. The remains, therefore, underwent an active transformation 

 into stone, or became, as we call it, petrified. Fossils thus transformed or 

 changed, are classed together under the name of petrifactions. 



This term is very often used as a synonym for fossils, but erroneously ; 

 because not every fossil has passed through a petrifying process, while there are 

 many belonging to younger formations, that have, outside of form and struc- 

 ture, retained also the color and organic matter of the original remains. Every 

 petrifaction is a fossil, but not every fossil is a petrifaction. The process by 

 which the transformation of organic remains into mineral bodies is produced, 

 is of a chemical nature, and depends upon conditions not yet fully under- 

 stood. 



We must distinguish between petrifactions and incrustations, although the 

 latter are often classed among the former. Incrustations are generally pro- 

 duced in springs, whose waters are charged with a considerable amount of 

 calcareous matter, which settles upon immersed bodies, like flowers and 

 branches, or shells and bones, inclosing them with a mineral coat or crust, 

 but never permeating them, as is done in the case of petrifaction. By break- 

 ing such incrustations we find, either the inclosed bodies unchanged, or, if 

 they have disappeared, the place formerly occupied by them *a hollow mould. 



Another transformation of animal matter is by many erroneously classed 

 among petrifactions. We sometimes notice in public papers reports of cases 

 where human bodies, resurrected after some years of interment, have been 

 found, not only well preserved in form, but so hard and stiff, and so much 

 increased in weight, as to appear completely changed into stone. Such cases 

 are looked upon by a great many people as a kind of miracle, while, really, 

 they are nothing more than the result of a chemical process by which the 

 animal fat has been converted into a sort of wax. Transformations of this 

 kind occur only in bodies buried in wet places, where they are completely 

 submerged by underground water charged with antiseptic ingredients. As 

 soon as these bodies are removed from their original resting place, they 

 commence to decompose, a fact clearly showing that they never underwent 

 the process of petrifaction. The wax-like material into which the fat is con- 



