Ixvi PROCEEDINGS OF THE GEOLGGICAL SOCIETY. 
Independently of the more ordinary modification of the vegetable 
substances constituting coal, Mr. Lyell pomts out another due to the 
Intrusion of matter im igneous fusion amid the coal-measures. At 
the southern extremity of the coal-field of Clover Hill, a dyke of 
greenstone is seen cutting through the coal and associated beds, alter- 
ing the coal into a kind of coke. At another point the coal was found 
to be also affected, bemg more or less deprived of its bituminous 
qualities. Mr. Lyell traced the igneous rock to within 120 feet 
of the coal in this instance, though he did not observe it in contact ; 
but he remarks that it may have more nearly approached the coal 
than he observed. There are also other instances of the same kind, 
reminding us of the effects produced upon coal in other countries, as 
in Scotland, where rocks in igneous fusion have filled up fractures, 
charring or coking the edges of coal-beds in immediate contact, and 
depriving them of oxygen and hydrogen, combmed with carbon, so 
that a bituminous bed of coal shades off gradually into anthracite as 
it approaches the imtrusive and igneous rock. 
The most remarkable example of the so-called natural coke was 
observed by Mr. Lyell at Edge Hill, a locality five or six miles 
north of the James es where a large quantity is extracted from an 
eight-feet bed.. The rocks passed thr ough, above the eight-feet bed, 
were 110 feet thick, and among them was a conformable bed of 
basalt 16 feet thick. The shale beneath the igneous rock was white 
for 11 feet, and then 25 feet of dark shale sueceeded, below which 
came the bed of: coke resting on white shale, and lower down coal- 
measures with two beds of inferior coal, each about 4 or 5 feet thick. 
The shale interposed between the basalt and natural coke-bed exhibits 
so many marks of rupture and friction, mcluding slickensides among 
the latter, that Mr. Lyell attributes the change from coal to ceke not 
s0 much to the heat of the intrusive basalt, as to its mechanical effect 
in breaking up the beds and rendering them permeable to water, or the 
gases of decomposing coal. He also points out, that where coke or 
altered coal reposes on that which retains its usual character, (as it is 
known to do in this coal-field, even the same bed having been found 
thus partially changed, the upper part altered and graduating into 
the lower,) the intrusive and molten rock, here as elsewhere, made 
its way among the beds, takmg the form of a conformable deposit, 
altermg the upper coal as far as its influence extended. 
These facts constitute good additional examples of the alteration 
of common coal by the intrusion of mineral matter in a molten state, 
and the Eastern Virginia coal-field seems to have been much broken 
up in some places, and molten rock forced among it. No doubt, as 
Mr. Lyell states, the fractured condition of the mass would readily 
permit the escape of the gases, which deprived the coal of its larger 
proportion of oxygen and hydrogen. The white condition of the 
shales beneath, or otherwise in contact with the igneous rocks, would 
also, if their dark colour elsewhere were due to carbon, be accounted 
for in the same way. The coke-bed may, from its analysis (carbon 
86°54; hydrogen 4:23; oxygen and nitrogen 4°53; ash 4°70), be 
considered in the chemical condition of an anthracite; many anthra- 
