710 
 seological wrmkles ;” and the troughs are divisible,into the west- 
ern and eastern groups. The former, having an area of forty-five 
miles by five, comprises the Shamokin and Mahony coal-fields, as 
well as the basin of Sheenandoah valley, with several small districts; 
and the eastern group, with an area of twenty miles by five, con- 
sists of the coal-basins of Beaver Meadow, Duck Creek, Hazle 
Valley; Black Creek, Bucks, Mountain, and MeCauley’s Mountain. 
From the frequency with which the conglomerate is brought to the 
surface, Mr. Logan says, it may be inferred that the middle region 
is shallower than the southern. 
The northern anthracitie region, bounded like the others by the 
quartzose conglomerate, is crescent-shaped, and includes the beau-~ 
tiful valley of Wyoming. Its length, from Carbondale to Knob 
Mountain, is fifty-five miles, but its greatest breadth is about four. 
Mr. Logan states that he took some pains to make a section across 
the northern region at Wilkesbarre, where the strata are less dis- 
turbed than in the two more southern regions. The total thickness 
of the measures, from the highest visible coal-seam to the quartzose, 
is stated to be about 2000 feet. ‘The upper part, comprising about 
650 feet, consists of argillaceous and arenaceous shales and sand- 
stones, with only thin seams of workable coal, and it is well exposed 
near Wilkesbarre: the middle portion, also containing about 650 
feet, is considered to be composed of softer materials, on account 
of its flatness; but its constituent strata are not exposed, and only 
one coal-seam four feet thick is reputed to occur in it. The lower 
measures consist of 700 feet of sandstones, with beds of shale, and 
they contain by far the most valuable coal-seams in the whole de- 
posit, amounting to fourteen or fifteen in number, with an aggregate 
thickness of seventy to eighty feet. ‘The most important bed, in- 
cluding interstratified shales and stigmaria beds, is thirty feet in 
vertical dimensions, but only eighteen are in general worked. 
In concluding this portion of his paper, the author states, that he 
had seen nearly the whole of the anthracite seams mentioned in it, 
and that with only one exception had he failed to discover under 
the coal, wherever he could get to the bottom of the seam, a bed 
of argillo-arenaceous materials, generally fit for the purposes of fire- 
clay, and filled with Stzgmaria ficoodes. The character of the bed, 
he says, is known to the more intelligent miners of Pennsylvania, 
as it is to those of South Wales, and is called by them ‘bottom- 
slate.” Professor Rogers, Mr. Logan adds, refers in one of his re- 
ports to a decided difference between “top-slate” and ‘ bottom- 
slate,” and, without alluding to the Stigmaria, remarks, that the 
“‘bottom-slate” is always composed of a strong tough material, 
having a peculiar splintery fracture, due, Mr. Logan says, to the 
vegetable remains; and he considers this observation of Professor 
Rogers an important collateral evidence in respect to the wide 
range of coal-deposits over which that geologist’s examinations 
“have extended. From information derived during personal com- 
munications with some of Prof. Rogers’s geological assistants, Mr. 
Logan has no doubt that the stigmaria underclays prevail in the 
great bituminous districts of Pennsylvania; and he has been given 
