FOSSIL PLANTS. 487 



nity to examine. Moreover, the silicified stems which have been noticed 

 above as marked by horizontal splits, are of the same compound in their whole 

 length. 



The silicified wood of the Coal Measures of Ohio, as that also of more recent 

 formations of our continent, furnish us some valuable data for the examination 

 of another vexed question : concerning their mode of fossil ization, or rather the 

 origin of the silica which has produced their transformation. Two opinions, 

 above all, have been advanced on this subject. Prof. Goppert thinks that the 

 process of petrification has been very slow, of long duration, and that to explain 

 it, it is not necessary to suppose that the water in which the vegetable sub- 

 stance has been transformed, was richer in silica than it may be now in its 

 normal state. Prof. Schimper, on the contrary, asserts that the water in which 

 wood has been silicified should have been of a higher temperature, more abun- 

 dantly saturated with silica, and therefore, he concludes that the kind of min- 

 eralization has happened in a much shorter time than is generally supposed, 

 and by volcanic agency, as is now the case in the vicinity of the Geysers of 

 Iceland. (1) To sustain this assertion, the celebrated professor says : that the 

 progress of the fossilizing process should have been rapid enough to reach the 

 whole substance of the wood before its decomposition by putrifaction. But 

 the woody tissue, when entombed and protected against atmospheric influence, 

 is unalterable for a considerable period of time, and slowly passes, by emere- 

 causis, into coal. It is, therefore, conceivable that in the first stage of this 

 slow burning, when the whole vegetable has been reduced to a soft matter, it 

 may be penetrated by mineral fluids which, by crystallization, transform it into 

 stone. In the valley of Locle, Switzerland, large prostrate trunks, more than 

 fifty feet long, were discovered some years ago in a bed of sandy clay of the 

 upper Tertiary. These trees, most of them Dicotyledonous, had their bark 

 still in a good state of preservation, their woody tissue admirably preserved, 

 and looked indeed as if they had been recently buried. Yet their wood was 

 soft enough to be cut through with the knife without effort, like butter. Beds 

 of lignites, in Germany, where the emerecausis is in a more advanced stage, 

 contains large trunks of wood, softened in the same degree, and already black- 

 ened. In that state, the woody tissues are easily impregnated by dissolved min- 

 eral substances. But to omit theoretical discussion and merely consider facts 

 observable around us, it is evident that our silicified wood, as well in our Coal 

 Measures as in the more recent formations, is found in connection with strata 

 which show no trace of volcanic agency. The silicified trunks of Southern 

 Ohio have been washed out by the creeks from the Mahoning sandstone. The 

 area covered by this formation, and over which the trunks are found in greater 



(1) Traite de Pal. Veget., p. 38 and 39. 



