GEOGNOSY AND GEOLOGY. 113 
long-continued disturbance of various rocks. One of these may furnish the 
whole supply, or several may be combined. They are known as granitic, 
porphyritic, syenitic, marly, tufaceous, calcareous, basaltic, pumiceous, &c., 
gravels. 
Series 5. Pebble Beds. 
These are distinguished from the last by the rounded character of the 
ingredients, and by their generally smaller size; the principal kinds are the 
ealcareous, silicious, and gem beds. Fragments of sapphire, topaz, chrysobery], 
as also pieces of gold and rare ores, are often found associated. 
Il. GENERAL OREOGRAPHY. 
The rocks, whose consideration, according to the systern of Hausmann, 
we have just completed, are those which, in greater or less accumulation, 
compose the crust of the earth. Great diversities, however, are exhibited 
in the manner of their occurrence, as well-as in the relations they bear to 
each other. The surface of the earth appears to present to us the greatest 
diversity of structure, in the most varied, and apparently irregular 
inequalities of elevation and depression; precipitous declivities, washed by 
rushing waters, rise up in fruitful valleys, and mountain ranges bound the 
_ horizon in the blue distance. Here are displayed smiling fields, or meadows 
embraced by noble forests cover the extended plains; there is seen a sandy 
waste, seemingly capable of supporting only the sparsest vegetation, while, 
in another place, jagged rocks stand out from cloud-capped heights, shutting 
out the beams of the setting sun. Seas, with foaming waves, wash away 
the coasts, and reveal the buried secrets of the earth. These irregularities 
and inequalities are, however, by no means accidental ; they proclaim great 
causes, which have thus modified the surface of the earth. Since stones or 
rocks compose the crust of the earth, and cause these irregularities, a 
new field opens to us in the investigation of rock formations (oreography). 
This department of our subject treats of rocks as they occur in great 
masses. Investigations of this kind have led to the most astonishing and 
stupendous results, in revealing to us the certain or probable action of 
mighty causes, in producing the effects we see around us. The solid crust 
of the earth is well calculated to exhibit the traces of expended forces ; not 
so with the atmosphere and the terrestrial waters. The hurricane may 
rage, and the waves be one moment heaped up mountain high, and the next 
sink down again into the abyss; lightnings may play and thunder roll; yet 
the waters when calm and the sky when clear, exhibit not a vestige of the 
commotions which agitated them. Not so with regard to the coast, whose 
incumbent rocks have been shattered by the surge, or the forest, whose 
vegetation has been mowed down by the blast; they (and the solid portion 
of the earth’s crust) alone present durable evidence of such mighty agencies. 
If, again, we examine the phenomena caused by volcanoes, where torrents 
of lava have annihilated blooming fields, where subterranean explosions 
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