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THE POPULAR SCIENCE MONTHLY 



fairly outlined ; but that these stumps and logs and splinters have 

 been wood there can be no possible doubt. Our microscope settles the 

 question once for all by revealing the very form and markings of the 

 original wood-cells now replaced by silex. In Fig. 1 we have the mi- 

 croscopic view of a section taken from a log lying on the summit of 

 one of the buttes. The medullary rays are plainly seen, as well as 

 wood-cells bearing series of peculiar concentric circles, which every 

 botanist instantly recognizes as characteristic of the Coniferce, the 

 cone-bearing trees, pines, cedars, firs, sequoias, so that we may not only 

 safely pronounce the petrifaction on the hill-top a fossil log, but we 

 have determined without doubt the vegetable order to which it belongs. 

 For the silicifying of such masses of organic material long submer- 

 gence was doubtless necessary, but to which of the beds of the series 

 exposed these relics belong it is difficult to determine. Such fossils 

 come to light only by erosion, and erosion leaves them always at the 

 lowest levels. 



But these are not the only evidence of a former vegetable life very 

 different from that now prevalent in the Bad Lands. All these beds 



Fia. 3. Platantjs nobilis (Newberry) x J. 



Fig. 4. Populous cttneata (Newberry). 



of lignite, said to exceed in area all the other coal-fields of the world, 

 are of undoubted vegetable origin. Knowing what we do about coal 

 in general, we can conceive of no other history for them, and although 

 we find in these American beds no such veritable logs as characterize 

 the hraun-Jcohle of Northern Europe, yet the presence in the lignite of 



