368 APPENDIX TO PARTS I AND II. 
shall endeavor to show, from a study of their contours, their geological structure and 
composition, their separation by a great valley, and their identity with the Alps and 
Jura of Europe, that they are sufficiently diverse to be known by different names. 
Distinctive Atlantic Features. These mountains occur as short, sharp ridges par- 
allel to one another in echelon arrangement. Their summit lines are irregular, and 
their peaks obtusely pointed. The culminating points are higher than those of their 
neighbors, reaching 6,300 in the middle and 6,700 feet in the southern sections. The 
rocks are ancient gneiss of Eozoic age, Laurentian, Montalban, and Huronian, with 
commonly inverted dips. The periods of elevation were mostly pre-Silurian. On the 
west side of the Green Mountains of Vermont and the Blue Ridge in Virginia, a portion 
of the earth-masses included with other systems consists of Silurian sediments standing 
at high angles. These are so involved with the gneiss as to indicate an elevation in 
Middle Silurian times. 
Distinctive Appalachian Features. Contrasting with the Atlantic elevations, the 
Appalachian ones occur in interminably long and narrow ridges, having level summits 
curving in the form of loops in the north, and terminating in pairs of straight ridges 
cut off short by faults in the south. Occasional gaps in them allow of the passage of 
roads. The elevation is usually 1,000 feet. The variation is from 800 to 2,500 feet; 
and in the Peaks of Otter in Virginia 4,000 feet is reached, in the neighborhood of the 
greatest elevation of the boundary valley. The rocks are altogether sedimentary, con- 
sisting of sandstones, shales, and a few limestones. They are curved, making the 
normal and symmetrical folds like a series of ocean waves. None of the dips are in- 
verted. They are Paleozoic exclusively ; and pebbles of the sandstone have often been 
derived from the breaking down of the crystalline schists of the Atlantic rocks to the 
east. The period of the elevation was at the close of Carboniferous time. 
Connected with this is the great plateau, commencing in Alabama and Tennessee, or 
the Cumberland tableland, with a mean elevation of 2,000 feet, and a width of 30 to 40 
miles. This is 3,000 feet high in Pennsylvania. It occupies a considerable breadth in 
central and southern New York, 2,000-2,600 feet high, and, highest of all in the Cats- 
kills, 3,800 feet. Here it terminates. It differs from the Appalachian mountains only 
in the smallness of the foldings, since in the coal plateau of Pennsylvania six basins, 
with the anticlinal arches between them, are described, and the same axes are pro- 
longed northwardly into New York. 
The Appalachians are divided along the Kenawha river in Virginia by a north-west- 
south-east fault, coinciding nearly with the highest part of the great valley. The Ke- 
nawha is the only one of the rivers flowing into the Mississippi valley that reaches and 
crosses the great valley. This break was produced bya great strain upon the crust, 
evidenced in the fall of the land northerly. It will be noted that the Atlantic moun- 
tains start with the culmination in North Carolina, and in northern Virginia divide, the 
one branch becoming the South Mountains in Pennsylvania, and the other sinks to the 
sea-level near Philadelphia. The low mountains of Staten Island indicate its place near 
New York. They rise into the White Mountains of New Hampshire beyond New York. 
