I9I3-] STEVENSON— FORMATION OF COAL BEDS. 99 



Reports on composition of coal show similar variations in all 

 coal fields. 



Some coals cake when heated, others do not. The available 

 methods of analysis lend no assistance toward explanation of the 

 difference. Some have supposed it to be physical, that the glance or 

 caking laminae are separated so completely by the dull laminae that 

 fusion becomes impossible ; but this can hardly be regarded as 

 established, for in some portions of the Connellsville basin, the coal 

 cannot be distinguished in hand specimens from the non-caking coal 

 of JMassillon, Ohio, yet it yields the standard coke. Nor does the 

 proportion of mineral charcoal seem to be important, since the 

 caking coal near Uniontown, Pennsylvania, has as much as some 

 non-caking coals of Missouri. It has been suggested that the Cre- 

 taceous coals of Colorado and New Mexico are caking in some 

 localities, non-caking in others, because of the nearness or distance 

 of igneous rocks. Unquestionably, there is much to be said in favor 

 of this suggestion, yet there is much room for the other suggestion 

 that possibly coincidence may have been mistaken for cause and 

 effect. It is not certain that the influence of dikes can be exerted 

 very far through coal or the accompanying rocks. Several of the 

 coal beds in southwestern Pennsylvania are of caking coal, while 

 there are others in the immediate vicinity whose coals are non- 

 caking. There is no reason to suppose that eruptive rocks have 

 exerted influence there. Incomplete conversion of the material as 

 shown by the action of caustic potash is supposed by some to account 

 for non-caking property, there are coals of Cretaceous age, which 

 are attacked energetically by caustic potash, yet make a firm coke. 

 The suggestion has been made that possibly the presence or absence 

 of sapropelic material may determine the extent of caking. This is 

 possible. 



The analyses by Carnot^*'" led him to interesting conclusions. 

 He procured i8 samples of coal from Commentry, representing sev- 

 eral genera of plants. Ultimate analysis showed that the elementary 

 composition of these coals is almost accurately the same throughout, 



^'^ Ad. Carnot, " Sur la composition et les qualites de la houille, en regard 

 a la nature des plantes qui Font formee," C. R., Vol. 99, 1884, pp. 253-255. 



