372 GEOLOGICAL SURVEY OF THE TERRITORIES. 



ures and in our tertiary and cretaceous formations in connection with 

 such strata, which do not show the slightest traces of disturbances and 

 of metamorphisin or change of nature by heat ; and at such localities 

 where no traces of thermal springs, or other phenomena of the same 

 nature, indicate the influence of volcanic action. 



When other substances, like clay, iron, sand, &c, have penetrated the 

 trees or plants subjected to fossilization, the internal structure of the 

 wood has been totally destroyed, and then nothing is left to indicate 

 its primitive nature but a thiu pellicle of charcoal surrounding the bark 

 and preserving therefore only the outline of the outer surface of the 

 trees. Trunks of this kind are often found either standing in their 

 original form, or prostrated and flattened by compression in the sand- 

 stone of our coal measures. The peculiar conformations of the trees of 

 this formation afford, from the scars of branches and leaves which have 

 been left on the trunks, the means of comparing them and of classify- 

 ing them, even according to their species. At some places, for exam- 

 ple, near the Eaccoon Furnace, in Northwest Kentucky, immense deposits 

 of iron ore have been formed by the accumulation of stems and leaves 

 of Stigmaria and Cordaites, which have been transformed into a rich car- 

 bonate of iron. The stems of Stigmaria have preserved their original 

 fdrm, not being flattened in the least, with the scars of their leaves 

 perfectly distinct, as well as the medular canal and its star-like divisions. 



When trunks are immersed for a great length of time in water which 

 does not contain any kind of mineralizing element, the softer tissue 

 becomes not only softened, but disaggregated in such a way that the 

 woody matter is separated like a paste, excepting the bark, which longer 

 resists this kind of disaggregation. In that way, and by compression, 

 layers of bark of species of trees of the coal epoch are found in the 

 shale, heaped upon one another in a more or less confused manner. The 

 same phenomenon is observable, even at our time, in some peat forma- 

 tions of the North, for example in Denmark, near the border of the 

 sea, in a large swamp out of which the peat is worked for combustible. 

 This matter is a half fluid paste, a compound of debris of woody fibers. 

 It is taken out in buckets, thrown upon beds of straw to drain off the 

 water, and then compressed and dried, when it becomes a good combus- 

 tible. In the meanwhile the bark of the trees from which this decomposed 

 matter has been derived is taken out of the ditch, like rolled, hollow 

 cylinders, and then dried separately and used as a combustible of less 

 value. 



It is especially from the petrification of leaves and small branches 

 that our valuable and interesting specimens of fossil plants are obtained. 

 Their fossilization is somewhat different from that of the trunks. Leaves 

 falling in pools of quiet Water, containing some muddy sediments, are 

 softened, then compressed, and by the hardening of the imbedding mat- 

 ter the skeleton of their tissue is printed upon the stone, sometimes in 

 its minutest details. In the shale of the coal-measures the matter of 

 the leaves has been transformed into a thin pellicle of coal, which shows 

 all the details of their structure. The exact outlines of whole fronds 

 of ferns, their leaves in their minutest divisions, the stems, the pedicels, 

 all the nerves and their branches, are there clearly printed in black upon 

 the stone, offering in their details of structure, characters which serve to 

 their determination. In some shale the leaves and branches are inclosed 

 in concretions or nodules of carbonate of iron, wherein they have left the 

 most beautiful and distinct impressions. Our tertiary and cretaceous 

 measures contain leaves of trees which are preserved in the same way, 

 in clay or soft sandstone, and which have left nothing on the shale bat 



