214 
Frocced'uHjs of the Royal Irkh Academy. 
teeth is sufficient to exclude the latter, of which they are the strong 
point. The bones are too large for the trout ; and on comparing the 
vertebrae with those of the sahnon the distinction is unmistakable. 
Erom the families of the Order Malacoptcrygii sub-brachiati we must 
choose the Gadoids. On comparing the vertebrae with those of one mem- 
ber of the family, the codfish, they were found to correspond exactly. 
"Whilst the pike, a river and lake fish, has been captured in the salt 
water below Derry, the codfish, I am informed, has sometimes come 
up above Derry with the tide, which ascends for many miles. Other 
Gadoids, the ling and whiting, have been captured in the estuaries near 
the city, and twenty miles from the main ocean. 
The discovery of these fish-remains, and the character of the 
deposit in which they were found, combine to show not merely that 
there used to be water here, but that this water was other than an 
ancient channel. The presence of a lough, extending over half a mile 
in width from the present river, is indicated. The physical conforma- 
tion of the place supports this view. The ground slopes suddenly in 
parts, forming a bank which appears to have been the shore of the lake. 
Almost from its base a floe-bog extends for over half a mile to the river 
channel ; and beyond the river, bog and alluvial clay indicate that the 
lough was enlarged more widely still. Its longer dimension was north 
and south, in the direction of the present river ; and in its course it 
appears to have been narrowed in places, and again to have widened 
out over the low levels. On looking north towards Derry, from 
Strabane Eailway Station or Lifford Bridge, little power of imagina- 
tion is required to revive the ancient scene. The hills and shelving 
shores enclose a vast and level expanse of bog and alluvium, through 
which the river winds, as though a living current were sweeping 
through the congealed waters of a great lake. 
The height above sea-level of the floe-bog, beside and beneath 
which this brick-clay is found, varies, near Ballymagorry, from 16 feet 
to 40 feet, according to the figures set down on the Ordnance Survey 
maps. If we examine the low ground bounding the river at both 
sides from Derry to Strabane, we find the following figures given as 
showing its elevation above sea-level in diff'erent parts : — 16 and 20 
near Derry ; 12 and 15 higher up ; 50 in one place, which probably 
was once an islet; 20 at the mouth of the Dennet ; 16 at Corkan Island ; 
16 at Island More; 18 and 13 near Strabane. Above Strabane and 
Lifford we have it 22 feet ; and along the banks of the Finn Eiver at 
16, 17, 14, 15 toward Castlefinn, where it is 19 feet. The floe-bog, 
indeed, lies between Strabane and Londonderry ; but gravel pits are 
to be noticed in many other places near the rivers, and the brick- clay 
is discoverable as far as Castlefinn. The preceding facts and figures 
combine to demonstrate that at a very recent period, geologically con- 
sidered, in place of the present Eiver Foyle, there extended from Stra- 
bane to Derry a long firth or irregular lake, of varying widths. 
Several islets studded its surface, jutting creeks ran in amongst the 
thickly- wooded shores, and a principal arm of the lake reached west- 
wards as far as the place where now stands Castlefinn. This now va- 
