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The first thing noticeable in approaching the city are the quarries in the side of the hills to the south, and these may be visited the first; they are but a short distance southeast of the station. Here the sandstone will be found in contact with the trap above and the layers of basalt, trap, tufa, sandstone, shales and conglomerates are exposed.
THE APPALACHIAN REGION. Where the Silurian system is most fully developed, from New York southward along the Appalachian Mountains, it comprises four series: 4 Salina . . . shales, impure limestones, gypsum, salt 3 Niagara . . . chiefly limestones 2 Clinton . . . sandstones, shales, with some limestones 1 Medina . . . conglomerates, sandstones
The hollows in some of the fragments of vesicular lava of which the breccias and conglomerates are composed are partially filled with calc-sinter, being thus half converted into amygdaloids.
His first exploits had been so noised abroad that the young men from the neighboring counties and the soldiers at home on furloughs would request permission to join in his raids. He could easily muster fifty of these, known as "Mosby's Conglomerates," for any expedition. The opportunity for developing his ideas of border warfare was thus presented.
Perhaps now and then the basins became long, brackish estuaries, whose low shores were swept by the incoming tide and were in turn left bare at its retreat to receive the rain prints of passing showers and the tracks of the troops of reptiles which inhabited these valleys. The Triassic rocks are mainly red sandstones, often feldspathic, or arkose, with some conglomerates and shales.
Two leagues beyond Piri, at Salapunco, the road skirts the base of precipitous cliffs, the beginnings of a wonderful mass of granite mountains which have made Uilcapampa more difficult of access than the surrounding highlands which are composed of schists, conglomerates, and limestone.
Some of these rocks look as if they had flowed as lavas over the bottom of the sea, and enveloped quartz pebbles which were lying there, so as to form conglomerates with a base of greenstone, as is seen in Lumley Den, in the Sidlaw Hills.
Once more, certain red conglomerates and grits on the north-west coast of Scotland, long supposed from their lithological aspect to belong to the Old Red Sandstone, are now identified with the Lower Silurians. These are a few instances of the small trust to be placed in mineral qualities, as evidence of the ages or relative positions of strata.
If the materials are coarse, as in grits and conglomerates, the same beds can rarely be traced many yards without varying in size, and often coming to an end abruptly. Section of sand at Sandy Hill, near Biggleswade, Bedfordshire. Height 20 feet. There is also another phenomenon of frequent occurrence.
A few leagues southward of these two places, on each side of the low primary range of S. Juan, there are some flat-topped, cliff-bounded, separate little hills, very similar to those fringing the primary ranges in the great plain south of Buenos Ayres: they are composed- -1st, of calcareous tuff with many particles of quartz, sometimes passing into a coarse conglomerate; 2nd, of a stone undistinguishable on the closest inspection from the compacter varieties of tosca-rock; and 3rd, of semi-crystalline limestone, including nodules of agate: these three varieties pass insensibly into each other, and as they form the uppermost stratum in this district, I believe that they, also, are the equivalents of the pure crystalline limestone, and of the red and white sandstones and conglomerates.
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