Page:The Journal of geology (IA journalofgeology11893univers).pdf/298

reous horizon occupying the central Mt. Washington plateau, and the locating of its boundaries (cf. map). Observations were then made a little to the north of Salisbury village which showed conclusively that the schist of that vicinity is below the limestone, the structure of the mountain at that latitude being essentially an anticlinal. On examining next the northern extremity of the mountain, observations were quite as conclusive in proving that the schist of Jug End is above the valley limestone, and that the section across the range at this latitude is essentially what Professor Dana has described. This knowledge that we have to do with two horizons of schist, the one lower and the other higher than the limestone of the Egremont valley, was soon followed by the discovery of lithological differences between the different beds, which have furnished the key to the structure. Topographical features soon suggested a course across the mountain through which the limestone might pass and separate the upper schist of the northern portion from the lower schist of the southern portion. Through this path the calcareous horizon of the Egremont valley, considerably modified it is true, has been carefully traced. A large number of observations have been gathered from all parts of the mountain mass. Each of the numerous peaks has been ascended and as many data as practicable have been collected. At this time the southern portion of the mountain had not been carefully studied. Later in studying the area lying to the east and southeast of the mass of Mt. Washington, it was found that the limestone of that section is divisible into two beds separated by a schist, which is lithologically identical with the lower of the two horizons of schist in Mt. Washington. The evidence supporting this and the manner in which the areal relations are illusive in the indications which they afford regarding stratigraphy, will be set forth in a later paper. The lower of the two limestone horizons was found to extend westward and disappear under the schist of the south end of Mt. Washington. The schist overlying it, which so resembled the lower of the Mt. Washington schists, was also traced along the northern border of the limestone into the southern portion of Mt. Washington. The areal