356 GEOLOGICAL SURVEY OF THE TERRITORIES. 



of cannel-coal in the lower part, topped by bituminous coal; or which at 

 one end are trite cannel-coal in their whole thickness, passing to bitu- 

 minous in following them to some other part of the same deposits, is 

 explained by these remarks on the formation of our peat-bogs. We lind, 

 also, a remarkable identity of compound in the bottom clay of the coal 

 and Lignitic beds, which, too, indicates by its remains the agency of 

 plants of a same nature or of Avater-plants in its formation. 



In comparing peat to coal, and judging from mere appearance, one 

 finds at first a great difference between these combustible materials. But 

 in following the intermediate grades which modify them according to 

 age, the iuterveniug links are found so intimately joined that it becomes 

 impossible to separate them or to mark divisions from permanent char- 

 acters. In ancient peat-bogs, the peat, especially near the bottom, 

 becomes black, compact, intermixed by layers of crystalline, though 

 still soft coaly matter, which only wants hardness to be comparable to 

 trii,e coal or even undistinguishable from it.* Passing from peat to 

 what is called lignite, or to deposits of woody matter in formations 

 older than ours, we find in these accumulations either beds of mosses 

 of species still recognizable as analogous to those of our times, or heaps 

 of trunks whose wood has still its color, its original structure, as it is 

 seen in the present peat-bogs, but which has already become softened, 

 to the consistence of clay. Some older deposits have their woody re- 

 mains, trunks, and branches, already blackened but still soft, being 

 easily cut by shovels. Still farther into the divisions of time or of 

 geologists, this wood, as at Golden, for example, is found hardened, car- 

 bouized-like, but preserving its original structure so distinctly that the 

 concentric layers of branches are as distinct as in the wood of our forests. 

 And in the same basin, or at the same horizon, as, for example, at the 

 Eaton, the combustible matter still. called lignite has become, by its ap- 

 pearance, hardness, and chemical compound, undistinguishable from the 

 coal of the Carboniferous measures. 



Chemistry accounts for the differences remarked in the various degrees 

 of decomposition of woody materials. It explains how the transforma- 

 tion of woody fibers into coal is the result of a retarded combustion by 

 the slow combination of the oxygen of the atmosphere with the hydro- 

 gen of the plants, converting the woody fiber into carbon and increasiiig, 

 proportionally to the duration of the process, the amount of fixed carbon. 

 In this operation of nature the wood passes through all the stages of 

 decomposition remarked in mineral combustible, from i)eat to anthra- 

 cite, &c. In the lignite the work is only half done, as seen in consult- 

 ing the numerous analyses given of this matter, which always indicate 

 a proportion of carbon relative to that of water or of as yet unburned 

 woody fibers. In some cases the slow maceration appears hastened to 

 its completion by subterranean heat. How else would it be possible to 

 explain the transformation of lignite into anthracite in close vicinity to 

 basaltic dikes, as at the Eaton Mountains and at Placiere Mountains, 

 New Mexico, when the same beds, at a distance, retain still the 

 appearance and chemical compounds of true lignite ? 



isTo thing is more admirable in nature than the apparently simple pro- 

 cess of the formations which have here been briefly reviewed. Nature 

 disposes of the carbonic acid of the atmosphere and of its humidity for 

 the food of the plants which, by a kind of digestion, elaborate it into 

 woody fibers. Under peculiar times and circumstances, where these 



* The bottom of a peat-bog of Locle, Switzerland, is formed of layers of this substance 

 already hardened and undistinguishable from iignite-coal. 



