SiGERSON — Fish-remains in Alluvial Clay of River Foyle. 219 
of Derry. At various places along this hollow the figures 18, 28, 28, 
29, 32, 36, 37, marked its heights above the level of the sea at low- 
water (the tide rises nine feet in Lough Foyle). JSTow, these heights 
were no greater than those recorded for the soil beside the (Upper) 
Foyle, where water once flowed. The physical appearance and geo- 
logical character of this furrow that crosses the neck of the Inishowen 
peninsula were next found to support the inference that it might have 
been a water-channel at the time of the existence of the Upper Lough 
Foyle. Captain Portlock well described the characteristics of this 
district (Ordnance Survey, Art. Detritus). The principal locality of 
the deposits which came under the head of Detritus lies about and 
includes Culmore. It runs inland (or towards S willy) from the Foyle; 
its edge is defined by the rise of the Schist range, the termination of 
which is covered with gravel. The inner part of this spacious flat is 
bog, resting on clay," he observes; and here again the resemblance to 
the Upper Foyle is marked. The edge at Lough Foyle is composed of 
thin horizontal strata of sand and pebbles. In other parts, this 
arrangement is not observed in the detritus ; the sand or gravel is 
heaped along the sides of valleys, the bottoms of which are flat bogs 
resting on level clay. " The union of these two forms of detritus im- 
presses strongly on the present surface the character of ancient water- 
courses, either lakes or rivers. The detritus of gravel narrows and 
defines the boundaries, while the level clay base contributes to give 
the boggy covering that uniformity of surface which characterizes the 
tranquil water of a lake." Such appearances may be observed in the 
valley which contains the bog of Shantallon, and bog and lake of 
Ballyarnet, where a chain of isolated sand hills may also be seen, up 
whose sides the bog has crept. Some of their summits have been 
capped by it within the memory of man. 
Then the furrow which crosses the neck of the peninsula is thus 
accurately described: — In the still more marked depression which, 
constituting the valley of Pennyburn, extends, with little variation of 
level, towards Lough Swilly, the appearances are equally illustrative; 
for, in advancing towards the west, the valley is narrowed between two 
beds, or islands of rocks, and exhibits a channel so natural and well 
defined that it is impossible to resist the feeling of being in a river or 
strait — an efi'ect which is greatly heightened by the level, smooth, and 
now grassy bog, which lines the bottom. The channel again swells 
into an open basin, and is again, for a short distance, contracted, as it 
winds round some projecting rocks, which seem to attest, by their iso- 
lated position, limited extent, and low level, that some powerful agent, 
such as water, had long exercised on them its abrading influence. The 
curious sandhill, called Dunberry Hill, is in the prolongation of this 
valley, and bears the same relation to it which those previously de- 
scribed bear to the valley of Ballyarnet." 
On investigating the subject historically, I find that portion at least 
of this transverse valley appears to have been a mere wet marsh in the 
nineteenth year of James L In an inquisition made that year, mention 
is made of a boundary marked by a river, " which river crosses over 
