THE CARBONIFEROUS SYSTEM. 175 



forming. This is proved by the fact that the blackband is full of the 

 shells of Estheria, a bivalve, aquatic crustacean. We know that at the 

 time of the formation of Coal No. 1 rivers flowed down from the north 

 into the coal basin, and there is little doubt that a tree uprooted on the 

 banks of one of these streams carried with it a fragment of the rocky 

 ledge on which it grew. Floating trees, holding stones in their roots, are 

 often noticed in our great rivers at times of flood ; and I have seen a 

 mass of gold-bearing quartz taken from the alluvial deposits of the Mis- 

 sissippi, near Memphis, which must have been brought from Wyoming 

 or Montana in the way I have described. 



On the preceding pages I have reviewed the geological structure of our 

 portion of the Alleghany coal field. The subject is one of considerable 

 interest, and it has been treated somewhat in detail, and yet it is so sug- 

 gestive and fruitful that it is necessarily imperfectly presented in this 

 chapter. The reports on the different counties that lie within the coal 

 area are more properly the media through which details of geological 

 structure are described. These are filled with facts which it is hoped 

 will serve to make this sketch somewhat more comprehensible than it 

 would be if it stood alone. 



The series of sections of the Coal Measures which I have prepared for 

 publication with this volume will, I think, make it easy to follow the 

 descriptions traced, and it is hoped that they will themselves afford evi- 

 dence in favor of the truth and fitness of the classification of our coal 

 seams which I have adopted, that will be far more satisfactory and influ- 

 ential than any argument. I think no one can follow with the eye 

 the common elements that run through these sections without being 

 convinced that there is more system and harmony in the structure of our 

 coal field thant some of our writers on the subject have been willing to 

 concede. 



I should say further, that the economical aspects of the subject now 

 considered — i. e., the arrangement, connection, reach, and identity of 

 coal seams, as also their chemistry and technology — -will form an impor- 

 tant part of the volume on Economic Geology, which, in due course, will 

 follow next in order to those now published. 



THE FAUNA AND FLORA OF THE COAL MEASURES. 



So much space has already been allotted to the geology of our Coal 

 Measures that little remains for their palaeontology. But this is a sub- 

 ject that belongs properly in another volume, and it will be considered 

 there more fully than would be possible in any circumstances here. I 



