222 
Proceedings of the Royal Irkh Academy. 
being at present elevated 149 feet 9 inches above the level of the sea at 
low water. At the period of its elevation the upheaval may have ex- 
tended to the Foyle basin also. 
Still it is scarcely needful to cite such a cause, even as assisting in. 
the obliteration of Upper Lough Foyle and the adjacent channels. The 
deposition of the travelled gravel and silts of which the tributary and 
often-flooded rivers and torrents were the vehicles, would proceed at 
no inconsiderable rate in such a lake. The great alluvial tract formed 
by the Rhone at the head of the Lake of Geneva, the removal of the 
lake margin to the distance of a mile and a half in eight centuries from 
the town of Port Vallais, the gradual tilling in of the estuaries of the 
Porth, Tay, and Humber, and of the Lee at Cork, all show what 
changes may thus be caused. Then the closing up of the west channel 
at the Island of Derry, by throwing all the weight of water on the east 
channel, caused it to be excavated to a greater depth. Four miles above 
Derry the river depth is only 22 feet; quite near it is only 24 feet; 
Avhile at the midst of the east channel it is 43 feet. 
This lowering of the escape channel would be followed by a low- 
ering of the lake surface at ebb tide ; and thus, by the partial uncover- 
ing of deposits, conditions favourable to the formation of marshes and 
growth of bog would be presented. The destruction of the forests, 
with which the locality was anciently well provided, would help in 
this respect, by diminishing the rainfall and decreasing the volume of 
the tributary streams. 
The obliteration of lakes, of which some examples in recent years 
have been noticed by geologists, has been several times mentioned by 
the ancient Irish annalists. And it is of importance, alike to geology 
and to history, to find that traces of the effaced lakes are yet discover- 
able, and that the methods to which their elfacement was attributed by 
the Annalists have been observed, in recent days, still in action. The 
following list contains the names of the principal vanished Irish 
lakes : — 
1. Burran. — The Island of Lough Burran was captured by O'Don- 
nell, A. D. 1544. The lake is now dried up, and ''the place called 
Loughaverra," in the parish of Ballintoy, county Antrim. — O'D. 
2. Ore. — This lake was last mentioned in the Annals a. d. 1143. 
Cam^)rensis calls its island '■^insula viventiumP A church was built 
on it. This lake is also dried up, and the ruins of the church are to be 
seen *'in the middle of a bog iu the townland of Monahinsha" (bog of 
the island), parish of Corbally, county Tipperary. — O'D. 
3. Feahhail. — Lough Foyle, already described. 
4. Gahhair. — The formation, or "eruption," of this lake is chro- 
nicled as having occurred a.m. 3581. The Loch and its islands are 
mentioned a. d. 933. It is now dried up, but the place still bears the 
name of Lough Gower, or Logore, in Meath. — O'D. The discovery of 
antiquities is recorded in "Proceedings, Royal Irish Academy," vol. i. 
5. Gair. — Lough Gur, as it is now called, was last mentioned in 
the Annals in 1599. It contained one large, well-fortified island, and 
