Page:The Journal of geology (IA journalofgeology11893univers).pdf/313

extended much beyond its present limit in a southerly direction. As the bed thins out it becomes more graphitic, indicating also that the conditions attending its formation had here some peculiar local characters.

Metamorphic Character of the Rocks as Indicated by Microscopic Studies.—The microscopic examination of thin sections of rocks from Mt. Washington shows clearly that they are strongly metamorphosed clastics. Evidence has been deduced from the secondary growths of feldspars, garnets, and tourmalines, as well as from the relations of the different metamorphic minerals to one another, to show that the orographic forces to which these minerals owe their development, operated in several more or less distinct periods.^[1]

Summary and Conclusions.—What has been set forth in the preceding pages agrees well with Professor Dana's views so far as the northern portion of the area is concerned. In the southern and central portions, however, where the areal and structural relations are more obscure, I have arrived at very different conclusions. This has been due, not to the discovery of errors in Professor Dana's observations, which have been in the main confirmed, but to the collection of a larger number of observations and to the application of some structural principles which were not made use of in his study. A glance at the map will show how perfectly the belt of Egremont Limestone which crosses the southern portion of the mountain, is concealed where it meets the valleys. This belt, the discovery of which furnished a key to the structure, is not at first apparent to the geologist, because at its ends the boundaries of the Riga Schist coincide closely in direction with and form and extension of the boundaries of the Everett Schist.

To summarize briefly the results which have been discussed in the foregoing, the Mt. Washington series consists of four members, which in order of age are as follows: 1) Canaan Dolomite, 2) Riga Schist, 3) Egremont Limestone, and 4)