684 Professor Sedgwick and R. I. Murchison, Esq., on the 



supposed from the evidence of sections) a true passage into the lower division 

 of the overlying trough. The only fact which could materially disturb our 

 proposed classification, would be the discovery of a series of plants among the 

 culm beds, unlike the fossil j^ora of the true coal-fields, and resembling the 

 fossil ^ora of some well-ascertained lower formation. But such a series 

 never has been, and we believe never will be, discovered in Devonshire*. 



The culm series, considered as a whole, cannot be properly classed with 

 the inferior groups ; as it has a distinct position, a different structure, and a 

 peculiar suit of organic fossils, animal as well as vegetable. It must there- 

 fore be represented, hereafter, on our geological maps by, at least, one distinct 

 colour. So far we conclude with perfect confidence. 



The enormous development of this series, the absence of the old red sand- 

 stone and mountain-limestone in their more usual form, and the fine slate 

 rocks in some parts of the lower culm group, may seem to make its geologi- 

 cal base somewhat doubtful. Again, the parallelism of position of the lower 

 group and the formations on which it rests (both on the north and the 

 south sides of the great trough), and its apparent passage into them, tend to 

 increase this doubt. Provisionally, then, and as a measure of caution, we 

 are willing to place the base line of the culm series in a geological position, 

 not yet perfectly defined. But, we repeat, no such ambiguity attaches to the 

 upper part of the culm series; as all the vegetable fossils derived from it, are 

 identical with published species, before obtained, from the true coal measures 

 overlying the mill-stone grit. 



Again, as the members of the whole culmiferous series (including both the 

 upper and lower divisions) appear to have originated in one uninterrupted 

 succession of operations, have a nearly common type, and partakeof the same 

 accidents, we certainly think that they must all be classed together. And if 

 this reasoning be correct, the lower groups of black shale and limestone (what- 

 ever be the supposed ambiguity of the base line) must also be classed with 

 the true carboniferous system. In its structure and in the paucity of its or- 

 ganic remains, it resembles the calp, or argillaceous limestone, at the base of 

 the carboniferous system of Ireland ; and the specific characters of its fossils, 

 as far as they go, do not invalidate but confirm the conclusion we have 

 drawn. 



* Some new facts have come to light (since the spring of 1837) connected with this subject, to 

 which we refer in the second part of this communication. 



