CONCLUSION. 



lu the district which has been considered in the above pages, we have 

 a comparatively regular arraDgement of the various geological forma- 

 tions. A continuation of the volcanic area first observed in 1873, has 

 been examined, and its southwestern borders Iiave been determined. 

 Adjoiniug that on the south is an extensive metamorphic region. Flank- 

 ing both the south and west are the sedimentary formations. Al- 

 though it is impossible in this case to retain any but the general outlines 

 of a classification heretofore used in the determination of volcanic rocks, 

 we are nevertheless enabled, by the regularity of occurrence, to parallel- 

 ize them to a certain extent. It is a notable feature that the eastern 

 portion of the volcanic regiou'is the older, while the western — the higher 

 one — is younger. In connection therewith, probably, is the fact ob 

 served that all outcrops of strata covered by the volcanics are un- 

 changed sedimentaries in the eastern, while they are metamorphics in 

 the western portion. This fact alone would, probably, prove to be a- 

 stroug argument in favor of searching for the point or points of outflow 

 in the western region. Considerable change in the niveau of the coun- 

 try must have taken place, to which allusion has been made in chapter 

 II. Although so many features of interest are presented at almost every 

 locality of the area, the larger portion of it, probably, centers in the 

 mining region. We have there the case of ore-veins of certainly Post- 

 Cretaceous age, traversing old metamorphic rocks, passing through them 

 and entering the volcanic beds that are regarded as Tertiary. Too lit- 

 tle is known as yet of the vertical distribution of ore in these veins to 

 admit of any generalizations on the subject, but it seems probable that 

 characteristic features regarding occurrence and frequency of the differ- 

 ent minerals constituting the ores will eventually be observed. The 

 regularity and uniformity in most characteristics that these veins pre- 

 sent, the rarity of dislocations or faults, point to their having been 

 formed either at or very nearly the same time. Since making the ex- 

 aminations in Baker's Park, the mining district of Lake Fork has been 

 more fullj- developed, and the discovery of a limited number of lodes 

 has been followed by many others that show fair indications of satisfac- 

 tory results. 



Difficult to study as the center of the metamorphic area may seem, 

 sufiicient evidence has been obtained near its borders to admit of a 

 reasonable explanation of their origin. It appears that the entire Silu- 

 rian series, and at many places a portion of the Devonian have furnished 

 the material for their formation. Pure sandstones would then produce 

 the quartzites that have given the name to that prominent group of 

 mountains, while other rocks with more alumina, magnesia, &c., account 

 for the granites and schists. Were it possible, on account of time and 

 the rugged character of the country, together with its superabundance 

 of rain, to make the requisite detail investigations, I think the question 

 might be fully solved and much applicable information gained. 



Mention has been made of the glacial phenomena observed in the 

 Quartzite group. Although they are limited to small areas their influ- 

 ence on shaping the drainage, and, by changing the surfaceof theground, 

 producing lakes and swamps, has been quite considerable. 



More varied in its single members than the preceding group is the 

 sedimentary portion of the district. Stratigraphically it is quite simple. 



239 



