1874.] 251 [Allen. 



effect upon the adjoining sandy strata very peculiar and interest- 

 ing. The portions nearest these fissures became thoroughly molten, 

 giving to the walls of these fissures glazed surfaces, vitrifying them to 

 a depth varying from half an inch to several inches. The melted 

 matter, in many cases, ran down in a viscous, semifluid state, solidi- 

 fying in pendent, flowing, rounded masses, or was squeezed out 

 through lateral cracks in the walls of the fissures and congealed in 

 botryoidal masses while still adhering to the walls. In some cases 

 masses occur that can be well described by comparing them to masses 

 of molasses candy that have been pulled and folded; as they exactly 

 resemble in structure and general appearance viscous matter that has 

 been pulled, twisted and folded while in a plastic state. A peculiar 

 and interesting change of structure is often presented by the sand- 

 stones immediately in contact with these highly metamorphosed 

 masses, a cleavage oblique to the planes of stratification being induced, 

 by virtue of which the sandstones break up into more or less regularly 

 five or six sided prisms, half an inch to an inch or two in diameter, 

 and one to two, and even two and a half feet in length. This pris- 

 matic structure was noticed at quite a number of localities, occurring, 

 in fact, wherever the sandstones and these little eruptive mounds 

 came in contact. 



Usually the areas of this intense igneous action present a very 

 broken and volcanic aspect, and a geologist suddenly transported to 

 one of these districts would feel at first that he must be in the midst 

 of a truly volcanic region. The blocks of scoriaceous material have 

 in many cases rolled down from the tops of the buttes and ridges, 

 and lie scattered in erratic masses from a single cubic foot in size to 

 those of a ton's weight throughout the adjoining valleys, and often 

 for some distance out on the level plain. These ragged masses of 

 volcanic rock crowning the higher points, with the adjoining deep 

 and abrupt ravines, combine to present quite a disturbed and chaotic 

 appearance ; yet a careful examination of even these localities shows 

 that the strata everywhere maintain their horizontality, save the 

 slight disturbances, of at most only a few yards in extent, already 

 noticed. The beds of cinders underlying the metamorphosed strata 

 point out most distinctly the cause and origin of the metamorphism 

 and the local disturbances of the strata. Occasionally, further con- 

 vincing proof that these eruptions proceeded from the burning of the 

 heavy lignite beds, and not from deep-seated sources, is afforded by 

 the occurrence of here and there the total removal of the mounds by 



