CHAPTER III. 



SEDIMENTAEY AEEA. 



After leaving the area covered by volcanic rocks, and traveling in a 

 southerly direction, the difference of geological formations can at once 

 be recognized from the confignration of the country. Instead of high, 

 rugged mountains, arranged in groups, without any reference to chain 

 or range systems, we here find a series of approximately parallel ridges, 

 tapering off gradually to the southern plains. While a great portion of 

 the volcanic district reaches above timber-line, the mountains or hills of 

 the sedimentary region are timbered, and the valleys between the ridges 

 show fertile, grassy soil. Although the variation in the lithological forma- 

 tions is not very considerable, it can, nevertheless, be readily recognized 

 from the orographic features of the country. Bordering immediately 

 upon the southern and western edges of the metamorphic area the sed- 

 imentary beds begin, extending from there south and westward, with 

 only small interruptions in the latter direction, caused by local volcanic 

 eruptions.- 



As stated in the chapter on metamorphics, the lowest members of the 

 geological series have almost entirely disappeared, leaving only small 

 remliants that cannot even be positively referred to any definite group. 

 A portion of the Devonian rocks have escaped the influence that meta- 

 morphosed underlying beds, and offer au interesting field for study, 

 partly on account of their contact with the metamorphosed material, 

 partly on account of local features they exhibit. Above them the Car- 

 boniferous formation sets in, greatly varied in its several members, and 

 retaining characteristic variations over a comparatively large area. 

 After this has been passed, a gap occurs in the adopted succession of 

 geological formations. The Triassic and Jurassic beds are wanting in our 

 district. Immediately above the Carboniferous the Cretaceous strata are 

 found, as it would seem from some exposures, resting unconformably 

 upon the former. These continue for a considerable distance down into 

 the plains, so far as our survey was extended, without being succeeded 

 by Tertiary deposits. 



SILURIAN. 



Only at one point a series of strata was found to crop out that might 

 be referred to this formation. Although no fossils were observed, and 

 the underlying formations had been thoroughly metamorphosed, the 

 overlying Devonian beds determine the view that they can be placed as 

 belonging to this formation. To the southwest of station 38, in the 

 caiiou through which Lime Creek finds its way, a succession of sand- 

 stone strata were passed, to which the above remarks refer. It is a 

 white, coarse-grained sandstone, deposited in thick strata, that dip at an 

 angle of about ten degrees to the southward at the point where they 

 were seen. Owing to the densely- wooded character of that portion of 

 the district, no satisfactory data could be obtained regarding the dip at 

 other points. This sandstone, which was observed at no other locality 

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