GEOLOGY AND MINERALOGY. 543 
After some preliminary observations upon the laws governing the distribution 
of sediments, and the accumulation of caleareous materials in geological formations, 
Mr, Hall proceeded to show that throughout the entire interval from the older 
Silurian to the end of the Coal period, the accumulation of sedimentary matter 
along the line of the Appalachian chain hac been far greater than west of it. 
He showed that in tracing some of these formations westward, they thin to one- 
tenth or even one-twentieth of their thickness in the east. 
During all this accumulation of 40,000 or 50,000 feet of sediments in the line 
of the Appalachian chain, there were evidences of shallow sea, in the fucoidal 
markings and mud eracks upon the strata. This great accumulation, therefore, 
could only have taken place by a sinking of the ocean bed during the period of 
deposition ; and this in accordance with what we know from the established laws, 
that the translation or removal of large amounts of matter from one part of the 
earth’s crust to another, will cause a depression of that part beneath which the 
accumulation takes place. 
He farther showed that such depression, occurring along a zone of two hundred 
miles in width and many hundreds in length, corresponding to the zone of 
accumulation, could not take place in a simple curve, but that the sediments, 
the laminz of which would slide over one another to a very limited extent, must 
become folded and contorted during the process, and that these foldings and 
plications, which would constitute numerous syrelinal and anticlinal axes, would 
have their longitudinal direction corresponding with the line of accumulation, or 
the line of the ancient transporting current. That these foldings and plications would 
gradually diminish in foree with their distance from the centre of the line of 
accumulation, and gradually die out with the thinning of the beds; this thinning 
depending on the original transporting force, which, gradually diminishing on 
either side of the great current, allowed the beds gradually to thin out. * * 
Subsequently these folded strata were subjected to the denuding action of 
water; and the foldings of the anticlinals, having broken or weakened their outer 
beds, made them subject to more extensive and extreme denudation, till these 
original ridges are now often the valleys, while the synclinals are the summits of 
the mountain ridges. 
Tn all the Appalachian chain it was shown that nowhere any evidence exists of 
the elevation of the mountain ranges by action or elevation from below. The 
erystalline or metamorphie condition of the strata was due to other causes, and 
he had shown that this metamorphism was coincident with the line of original 
accumulation; and in greater or less degree coextensive with the folded and 
plicated beds; its incipient stages being visible in the first gradual or gentle 
foldings of the strata outside the great disturbed and crystalline zone. 
In the Mississippi valley, where there is no important folding or plication, we 
have outliers of these strata, or mounds, as they are termed, measuring one 
thousand feet of elevation above the Mississippi valley, the fundamental rock 
there being the Potsdam sandstone. In the Appalachian chain we find no rock 
of older date than the Potsdam sandstone, and this is seen only on the flanks of 
the chain, or rarely elsewhere, but the mountains rise to four, five, or six thousard 
feet above the sea. In the Mississippi valley the measurement of elevation is the 
