Reviews—Richmond Coal-field, Virginia. 139 
are beds once exposed in mines now closed which tend to give 
support to the opinion just quoted. 
_ The deduction, that the rock material was deposited on a steep 
slope, in all probability will not stand searching investigation. 
There is far too much stress put upon the assumption made by Lyell, 
and since then unquestioned, that the present basins were basins at 
the beginning of the Triassic, and that the irregularities are due to 
deposition on uneven surfaces rather than to subsequent bending and 
crushing. The evidence, on the contrary, points to the fact that this 
coal series was deposited in a horizontal position. Not enough 
allowance has been made for the effect of subsequent crushing and 
erosion of these soft rocks. 
It is well known that one of the principal coal beds, dipping at 
an angle averaging 30°, has been worked along the strike for, say 
a mile, and has been explored on the dip for 1500 feet, equivalent to 
a vertical depth of 750 feet. Throughout this breadth of 1500 feet 
it maintains approximately a uniform thickness. Surely no theory 
can satisfactorily explain this uniformity of thickness through such 
a vertical range, without admitting the original horizontality of the 
coal floor. The author of the paper cannot have carefully considered 
his position when he says, ‘The coal seams in the main basin are 
equally thick at the outcrop and in the deep; the tenacity of the 
roots having given the coal plants a firm hold up the steep sides of 
the trough.”! Not only the uniform thickness of the coals on the 
dip, but the lamin of shale between the coals, the fire clays and 
impure limestones between the beds, all testify to the original 
horizontality of these beds. And the innumerable “troubles,” as 
the areas of crushing and faulting are locally called, give the 
strongest proof of the enormous subsequent movements. 
A conclusion of great practical importance depends upon the 
confirmation of this set of facts—and this is the persistence of the 
coal throughout the bottom of the main basin. If it is conceded 
that the strata do not thin at the outcrop, and that they were 
deposited on horizontal surfaces, then all the hypotheses of Lyell, 
Lesley,’ and others, based on the supposition that the bottom of the 
present basin was under different conditions of depth and water 
currents from the present sides, fall to the ground, and we have no 
reason to suppose that the beds in the centre of the basin differ in 
original characteristics as to number, thickness, and continuity of 
coals from those at the outcrop. 
It does not follow from what has been said that any one workable 
coal is continuous across under the basin to the outcrop on the other 
side. On the contrary, this is probably not the case. ‘The identifica- 
tion of any one coal seam for a distance of even one or two miles is 
a matter of great uncertainty, owing to the number of the seams, 
the changes in the thickness both of the coal and accompanying 
shales, the bending and crushing to which all have been subjected, 
1 Page 7, idem. 
2 Quoted in McFarlan’s ‘‘Coal Regions of America,” p. 512, from Lesley’s 
U.S. Railroad and Mining Register, Philadelphia. 
