44 wW.S. GRESLEY—CLAY-VEINS INTERSECTING COAL MEASURES. 
ance of the underclay of the coal bed through which it passes, which 
has been squeezed or caused to flow upward into an open crack. A 
singular feature of this clay-vein consists in the very curious overlap of 
the vein to the left on gaining the roof of the coal, where it would seem 
that the intrusive clay at this place met some obstruction, which diverted 
it and caused it to curl over and actually penetrate the upper layers of 
the coal bed in the manner shown. 
Again, some of the sketches furnished by Mr Campbell, from his own 
careful observations in the Kanawha coal region, make it appear that the 
clay-veins penetrating the lower part of the seam only are injected or 
intrusive veins. 
That many of the socalled “spars” were formed or filled with clay, 
sand, and other materials by mechanical force seems highly probable. 
FOSssILIFEROUS VARIEGATED NopULES IN CLAY-VEINS 
In a well defined and persistent clay-vein, at a depth of about 100 feet 
in the Pittsburg coal, at Buena Vista, Allegheny county, Pennsylvania, 
there occur some singular boulder-shaped, very 
hard masses of rock, two of which are shown in 
the middle of figure 14. The vein stuff at this 
horizon is composed of a mottled and varie- 
gated, closely compacted breccia of small rock 
fragments of sundry kinds, with a few larger 
lumps of coal in contact with the nodular 
masses. ‘The appearance of this vein material 
suggests that 1t has undergone considerable 
mechanical and chemical alteration, as the 
component bits of rock are usually elongated, 
flattened, or drawn out, and have a rather run- 
together, viscous, or kneaded aspect. A frag- 
ment broken from one of these balls had a kind of shelly or easily 
spalled exterior, the flakes being about a third of an inch thick, while 
the interior of the nodule was very hard and compact, showing a few 
radial spar-filled cracks near the center. 
The composition of this nodule, both as to body and shelly exterior, 
is brecciated and variegated, and it shows evidence of chemical alteration, 
in that certain spots seem to have been converted into a reddish, streaky 
rock, while other areas reveal their original fragmentary structure much 
more plainly. The cementing and altered material seem to consist largely 
of silicate of alumina and lime, with irregular plays and crystalline nests 
Figure 14.—WNodules in Clay-vein. 
One-sixtieth natural size. 
