Allen.] 250 [January 21, 



heavier lignite beds must of course be very great, and the pressure 

 they must exert when thus pent up be by no means inconsiderable. 

 In regions where the greatest intensity of igneous action has oc- 

 curred, or where lignite beds of four to six or more feet in thick- 

 ness have been burned out, there are frequent evidences of the 

 breaking through to the surface of these subterranean fires. These 

 evidences consist of jagged, chimney-like mounds of volcanic breccia 

 that crown many of the buttes and ridges, the softer materials that 

 surrounded them having been worn away by denuding agencies, leav- 

 ing them as striking and picturesque features of the landscape. 

 These chimney-like mounds are often circular, and but a few feet in 

 diameter, but sometimes are prolonged into narrow wails of ragged, 

 lava-like rock, presenting the features of a true volcanic breccia. 

 Most of the matter composing these chimneys presents the appear- 

 ance of having been forced out through small orifices or narrow 

 fissures while in a semi-molten or highly plastic condition. In con- 

 nection with these ejections there were occasionally slight disturb- 

 ances of the adjoining strata, affecting sometimes an area of only a 

 few feet in diameter, and rarely extending beyond a few yards. 

 They were little volcanic puffs, — volcanoes, as it were, in miniature, 

 — having their seat of action in the burning coal-seam, ten, fifteen, 

 or perhaps fifty feet below. The molten or plastic matter in its pas- 

 sage often carried with it angular pieces of the adjoining strata, 

 which, becoming consolidated with the melted mass, form the brecci- 

 ated matter already mentioned. These chimneys, as before stated, 

 are often but a few feet in diameter, and sometimes but a few feet in 

 height. At other times they form masses ten or fifteen feet in diam- 

 eter, and fifteen to twenty feet in height. They are generally irregu- 

 larly scattered, and vary, in respect to distance from each other, from 

 a few feet to fifty or a hundred yards, or even greater distances. 

 Those occurring in the same immediate vicinity are generally of 

 nearly the same size, some districts being characterized by small 

 mounds of this character, others by large ones ; the size being propor- 

 tioned to the thickness of the lignite bed, to the burning of which 

 they owe their existence. 



Considerable portions of the matter composing these mounds is 

 highly vesicular, or presents an eminently scoriaceous character, but 

 often associated with it are the beautifully-variegated jaspery varie- 

 ties of the igneous material already described. The heat was, of 

 course, exceedingly intense at these points of eruption, and its 



