74 REPORT—1848. 
On the Geology of Pennsylvania. By Professor H. D. Rogers. 
Professor Rogers exhibited a general map of North America, the State Survey of 
Pennsylvania, and many other maps and sections coloured geologically. 
1. After pcinting out the general accordance in the succession of the older rocks 
in America with those of Europe, he stated that the rocks composing the great 
Appalachian chain had been deposited near the eastern shore of the Palaeozoic Sea 
in North America, and detailed a variety of circumstances in evidence of the exist- 
ence of an ancient continent in the direction of the Atlantic. 
2. Amongst these hills there is a well-defined series of rocks, containing a suc- 
cession of fossils ; but further west, where the same strata spread out to an enormous 
extent (in Kentucky and Tennessee), we seem to have arrived at the deep-sea part of 
these formations, in which all distinctions melt away, and an uniform succession of 
sedimentary deposits have accumulated to a much greater thickness than near the 
coast. Wherever the tributaries of the Ohio, or the rivers of Virginia break through 
the hills, we find beds of grit diagonally stratified, with conglomerates and all other 
indications of a shallow sea; but passing westward the same beds become finer and 
finer, the conglomerate passing into grits and these into fine-grained sandstones. The 
carboniferous limestone, which is but a few feet thick in the Appalachian, becomes 
500 feet thick in the Mississippi. 
3. After the elevation of the greater part of this region, the sea still covered the 
whole of Florida, the great plains of Arkansas, and extended far up the Missouri, and 
along the Atlantic plain as far as New Jersey; over this area was deposited first the 
cretaceous series and afterwards the tertiary. 
4, Between the tertiary plain and the-Appalachian hills is a great tract of un- 
fossiliferous rocks (“ Azoic” and “ Metamorphic”), at least 10,000 feet in thickness, 
and along their western boundary, fur 100 or 150 miles, the newer rocks all dip under 
them. This extraordinary circumstance was first explained by Professor Rogers, who 
has shown that it is the result of the felding of the rocks. The Appalachian chain 
consists, in fact, of a series of parallel anticlinal and synclinal folds, all leaning over 
to the west, so much as to invert the series of beds on the west of each synclinal ; 
these folds are steepest where they plunge beneath the azoic series, and open out 
gradually westward, until the strata become horizontal in the Ohio coal-field. 
Professor Rogers then gave a summary of his theory of the origin of these great 
parallel foldings in the Appalachian strata, which he attributes to a series of earth- 
quake movements, flowing forward in a particular direction in parallel lines; and he 
illustrated this view by a description of three remarkable earthquakes in the year 
1833. The first, that of St. Domingo, was experienced by the officers of a British 
vessel at sea, who stated that looking at the coast they had seen “ the crests of the 
hills waving like the back of a serpent in gentle motion;”’ these undulations had 
been traced along lines on which they were synchronous. 2. The earthquake in the 
Vale of the Mississippi, in which the lines of synchronous shock ranged N.N.E. and 
S.S.W. for 500 miles; at a parallel 300 miles east of the line the shock was ex- 
perienced eight minutes later; and all along the Atlantic shore twenty minutes 
later. The sensation was not that of a harsh grating of subjacent rocks, but a 
billowy heave. 3. A few months later another earthquake affected the whole vol- 
canic line of the Windward Isles and Bermuda simultaneously, and was attended by 
a sudden return to activity of some of the dormant craters; in the course of twenty- 
two minutes it had flowed to the United States, and rocked the whole coast from 
Florida to New York. All these phenomena were considered to prove the doctrine 
of a flexible crust resting on a fluid nucleus; and, as in former times, the crust may 
have been more flexible and the volcanic forces more energetic, the whole surface 
may have been thrown into billowy undulations, and there have become permanently 
fixed by the successive injection of lava into the craters and fissures of the varicus 
folds, thus preventing their return to horizontality. 
5. The three great coal-fields of America are, that of the Ohio, 740 miles long, and 180 
wide, covering an area of 63,000 square miles, a surface greater than that of England 
and Wales; the Illinois coal-field, covering 50,000 square miles; and the Michigan, 
occupying 15,000 square miles. Besides these, there are numerous anthracitic 
basins in Pennsylvania and Virginia, the furthest being 100 miles S.E. of the margin 
of the Ohio coal-field. In passing across these coal-fields there is a gradual diminu- 
