NATURAL HISTORY. 
granular in texture, and analogous in structure to the schist—thin, white, crystalline stripes being 
visible on the cross fracture, though they are not sufficiently continuous to affect the cleavage. 
The greenstone is dense, close-grained, and homogeneous, and is met with only at Conn’s Hill 
quarry, which (strictly speaking) is without the parish. The mode of its arrangement in respect to 
the schist cannot be seen in this quarry, but will be described in other parishes. It is traversed by 
several veins of quartz, which have much of the character of metalliferous veins, though they are 
thin, and do not exhibit any important metallic ore. 
New red sandstone is seen to a small extent on the little stream, which bounds the parish and 
the county on the N. It is too much concealed by the detritus to be traced to its junction with 
the great mass of schist on the W. of it: but, when its appearance in a similarly confined space is 
considered—in Clondermot on the S. E. of the parish, and beyond Muff, iu the county of 
Donegal, on the N., as well as on the shore on the N. E. —there can be little doubt that it either 
does extend along the whole face of the schist range, though now concealed in detritus, or did so 
formerly. Near the spot pointed out the slate has a loose, shaly structure, very similar to that 
which it possesses in places where it is decidedly in contact with the sandstone, as will be shown 
in subsequent parishes. 
Section 1.—Sub-section 2.— Detritus. 
Detritus ..—The consideration of the varied deposits, which come under this head, is always 
replete with interest. In this parish they occupy only a small space—the principal locality being 
a patch at the north-eastern angle of the Liberties, including Culmore Point. It is bounded on 
one side by Lough Foyle, and extends into the county of Donegal on the other, its edge being 
defined by the rise of the schist range, the termination of which is concealed by an accumulation 
of gravel. The inner portion of this spacious fiat is bog, resting on clay, the surface of which 
has been to a considerable extent reclaimed. The edge at Lough Foyle is an elevated bank, com¬ 
posed of sand and pebbles, which often exhibits a very striking regularity of arrangement, hori¬ 
zontal layers of sand being interposed between others of pebbles—the latter varying in size 
from 1 to 8 or 9 inches. They are of two kinds:—1st. Rocks not immediately found in the 
parish, such as granite; gneiss; primitive greenstone, approaching to hornblende rock ; and 
quartz rock. 2nd. Rocks common in the vicinity, such as the several varieties of schist. These 
constitute by far the greater proportion of the whole. The pebbles are rounded, but usually have 
flat bases, on which they rest, such being a natural consequence in rocks of schistose structure. 
Approaching Muff (in the county of Donegal) the pebbles are observed to overlie the clay sub¬ 
stratum of the bog, while the resemblance they bear to the pebbles now on the beach is striking, 
though, to a certain extent, it might have been expected—the wearing-down of the banks having, 
without doubt, supplied many of the latter. 
The central portion of this detritic flat is principally clay of a reddish hue, and so strongly 
resembling some of the beds, which in Faugiianvale alternate with the red sandstone, as 
further to corroborate the opinion already stated—that rocks of that formation either extended once 
over the whole space, or still underlie it. On the surface of this clay water accumulates, which, 
percolating the girdle of sands and gravels, that in part surrounds it, supplies the springs, which 
either trickle from the bank, or appear in shallow holes made by the country people in the sand on 
the shore of the lough, a little above high-water mark. 
The only other deposits of this kind are small patches of clay, which here and there border 
the Foyle. These have resulted from the decomposition of the slate rocks, and gradual washing- 
down of the finer particles: they are of very recent origin, and still augmenting. A drain, cut 
through one portion, exposes horizontal logs of oak—while in others, near the surface, there are 
numerous small tubular bodies of a conical form, apparently the encrusted roots of plants, and the 
rubble of an old brick-yard, abandoned only about thirty years ago, which was thrown on the 
shore, is now covered with 8 inches of soil. However, as might have been anticipated, what 
is formed at one period is destroyed at another, according to the direction of the current, which, 
while the banks of the river are subject to wear, must be ever varying; and embankments are, in 
consequence, found absolutely necessary to secure from destruction the now projecting points. 
But, though in other parts of the parish the detritus has not assumed that definite arrange¬ 
ment, which would entitle it to be considered as a distinct formation, it deserves attention, as 
having an evident bearing on the general phenomena of the district. It may be noticed as gravel 
and sand, heaped on the sides of the principal valleys—or as clay spread over the greater portion 
of the plains and hollows, which either were formerly or are now covered with bog. The union 
of these two forms of detritus impresses strongly on the present surface the character of ancient 
water-courses, either lakes or rivers. The detritus of gravel narrows and defines the bounda¬ 
ries, while the level clay base contributes to give the boggy covering that uniformity of surface, 
which characterizes the tranquil waters of a lake. Along the valley, which now contains the bog 
c 
