i ey 
104 PROF. GROOM ON THE CAMBRIAN AND [Feb. 1902, 
(6) Lithology. 
Except where bleached or indurated by igneous action, the beds 
of the zone of Spherophthalmus alatus are almost always soft, very 
fine-grained, minutely micaceous, fissile, black or coal-black, or very 
dark-grey shales, so closely jointed as to break at the slightest tap 
into small tabular pieces. It is, in fact, almost impossible to obtain 
a durable specimen of even moderate size. 
The grits of the zone of Polyphyma vary from medium to coarse 
grain; they are practically in the condition of quartzite, often with 
concealed joints. The fragments consist chiefly of quartz, meta- 
morphic quartzite, and decomposed felsites. Glauconitic casts of 
foraminifera are present in fair quantity. The finer-grained 
varieties closely resemble the dark quartzites of the Hollybush 
Sandstone. 
In the village of White-Leaved Oak an almost identically similar 
rock was used, evidently many years ago, for road-metal. It differs 
from the grits described above in the prevailingly somewhat finer 
grain, and could hardly have been obtained from the locality in which 
these are found, inasmuch as they can be reached only by excavation 
in an old pathway and are not present in sufficient quantity to 
furnish road-metal. But I failed, after assiduous search and inquiry, 
to trace the road-metal toitssource. At first, it seemed possible that 
the rock belonged to the Hollybush Sandstone Series, in which there 
is much dark-grey and black sandstone; but no sample of the sand- 
stone precisely resembling this black grit could be found, and I finally 
obtained from the road-metal pieces of grit with Black Shale still 
clinging to the bedding-surface—a clear proof that the grit belongs to 
the White-Leaved-Oak Shales. In all likelihood the road-metal came 
from the shales of the village-road itself, and I think it possible that 
it is in situ. We have, then, some evidence either that a patch 
belonging to the zone of Polyphyma has been faulted-up into the 
overlying shales near White-Leaved Oak, or that grits similar to 
those of that zone occur also in the zone of Peltura. 
(c) Relation to Underlying and Overlying Formations. 
The striking contrast between the Hollybush Sandstone and the 
White-Leaved-Oak Shales seen everywhere, even along the line of 
contact, and the circumstance that along the greater part of this 
junction the Hollybush Sandstone is of the dark type supposed to 
characterize a low horizon in the formation (see p. 96), suggests 
that beds are missing along the line of contact, owing either to 
unconformity or to faulting. The recent discovery at the northern 
extremity of Chase-End Hill of the grits of the Polyphyma-zone 
(see p. 100) appeared to suggest that the beds containing them 
might be near the base of the Black Shale Series; but the possible 
