452 Reviews and Notices oj Books, 



searches into the origin and composition of the " mineral char- 

 coal," and "compact coal" of the carboniferous system. 



"A consideration of the decay of vegetable matter in modern 

 swamps and forests shows that all kinds of tissues are not under 

 ordinary circumstances susceptible of the sort of carbonization 

 which we find in the mineral charcoal. Succulent and lax par- 

 enchymatous tissues decay too rapidly and completely. The bark 

 of trees very long resists decay, and, where any deposition is pro- 

 ceeding, is likely to be imbedded unchanged. It is the woody 

 structure, and especially the harder and more durable wood, that, 

 becoming carbonized and splitting along the medullary rays and 

 lines of growth, affords such fragments as those which we find 

 scattered over the surfaces of the coal. These facts would lead 

 us to infer that mineral charcoal represents the woody debris of 

 trees subjected to subaerial decay, and that the bark of these 

 trees should appear as compact coal along with such woody or 

 herbaceous matters as might be imbedded or submerged before 

 decay had time to take place. 



" The method of preparing the mineral charcoal for examination 

 was an improvement on the " nitric-acid " process of previous 

 observers, and the results gave very perfect examples of the disc- 

 bearing tissue restricted in the modern world to conifers and 

 cycads, but which existed also in the Sigillariae of the coal period. 

 With this were scalariform vessels, like those of ferns and club 

 mosses, and several other kinds of woody tissue. On careful com- 

 parison it was found that all these tissues might be referred to the 

 following genera of plants common in the coal measures : Sigil- 

 laria including Stigmaria, Calamites, Dadoxylon and other coni- 

 fers, Lepidodendron, Ulodendron, ferns, and possibly some other 

 less known plants. 



"Another form of tissue observed was a large spiral vessel, pos- 

 sibly belonging to some endogenous plant. 



" The structures preserved in the layers of shining compact coal 

 are more obscure, and I therefore present a somewhat more full 

 summary of the facts known in respect to them : — 



" The compact coal, constituting a far larger proportion of the 

 mass than the " mineral charcoal " does, consists either of lus- 

 trous conchoidal cherry or pitch coal, — of less lustrous slate coal^ 

 with flat fracture, — or of coarse coal, containing much earthy mat- 

 ter. All of these are arranged in thin interrupted laminae. They 

 consist of vegetable matter which has not been altered by siibae- 



