that are given to them denote their general character rather 

 than their precise constitution. Vegetable tissue of all kinds, 

 consists essentially of about one-half carbon and one-half hy- 

 drogen and oxygen gases, with small amounts of nitrogen and 

 some other elements which need not be here considered. In 

 the change to peat or lignite, the proportion of carbon has risen 

 from 50 per cent to (lO or more. The bituminous coals range 

 from some 60 to 75 per cent of carbon; then come the inter- 

 vening grades known as semi-bituminous and semi-anthracite, 

 with increasing carbon content, and finally the true anthracite, 

 with 80 to 90 per cent or even more, of carbon remaining; then 

 follows graphitic anthracite, and finally graphite, which is 

 nearly pure carbon. 



In the series now placed on exhibition, these several grades 

 or stages are represented by characteristic specimens, arranged 

 in order, from Sphagnum moss uj) to graphite. The pressed 

 mosses show somewhat the darkening and dying of the lower 

 portion of the stems. Then are seen several examples of peat, 

 beginning with very raw, pale-brown, salt-marsh peat, such as 

 abounds at many points along the coast — a mere loose mat of 

 half-decayed fibres — and passing on through various grades of 

 lignite, soft coals, and hard coals, to graphite as the closing 

 term in the series. The labels explain the character of each 

 specimen and enable the student to follow the process. 



The Oils and Asphalts 



Another type of carbon minerals is found in the asphalts, 

 bitumens, and oils. These are hydro-carbon compounds con- 

 taining little or no oxygen. The precise manner of their origin 

 is not so well known as in the case of the coals; and it seems prob- 

 able indeed that they may have been formed in several dif- 

 ferent wavs ; but in all cases doubtless from organic matter, ves- 



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