SiGERSON — Oti the Physical Geography of Irdami. 2l 



greatly subjected to the influence of seismical action. The following- 

 conclusions may be di'awn : — 



1st. The descriptions given in the annals, or woven into legends, 

 of the various physical phenomena mentioned coincide closely 

 with what we know, in a siu'e manner, of the results of earthc^uake 

 action in modern times. 



2nd. The evidence of earthquake action in Ireland, given thus 

 unconsciously as to cause by our ancient annalists, is doubly valuable 

 because of its proven accuracy and undoubted antiquity. 



3rd. Our ancient records form, probably, the largest collection of 

 ancient seismical indications and results now in existence. 



4th. Ireland was, of old, extremely subject to the influence of 

 earthquakes within histoiical times. 



5th. By comparing our ancient with our modern records, we have 

 a means — wanting in most, if not all, countries besides — of noting 

 with approximate accuracy the increase or decrease of seismical energy 

 in a given area. 



When the ^-eat convulsions, tailing ofi', gradually diminished in 

 frequency and intensity, the principal physical changes which after- 

 wards took place were those attributable to common causes usually 

 seen in operation. In some cases, by the gradual silting up of straits 

 and channels, and by the growth of bog, islands have been xmited to 

 the mainland. Instances may be found in the case of Malin, formerly 

 insulated; of Innisho wen, formerly insulated; of the Isle of Doagh, and 

 of the Isle of Inch (both in Lough S willy) ; of Horn Head, the Isle of 

 Derry, and of several islets on the north-west coast. According to 

 the observations of Professors Sullivan and O'Eeilly, the Hill of 

 Howth was also formerly insulated. 



Alterations in the physical geography of the country have also 

 taken place by the obliteration of lakes, wrought by deposit of allu- 

 vium, by evaporation, or by migration of the waters of the lake 

 rupturing their boundary (of which America offers recent instances). 



The following are the names of the lakes whose former existence 

 I have traced, and whose places are now occupied by bog or dry land : 

 Loch Burran, now called "Loughaverra," in the parish of Ballintay, 

 Antrim; Loch Cre, the island of which now occupies the centre of a 

 bog in the townland of llonahinsha (bog of the island), in the parish of 

 Corbally, Tipperary ; Lough Foyle, now represented by a river (still 

 called "Lough Foyle"), extending between Strabane and Derry; 

 Loch Gabair, now Logore, in Meath; Loch Gair, now Lough Gur, 

 Co. Limerick, still a lake, but of diminished size, as its island has be- 

 come attached to the mainland ; Loch Laeghaire, south of Strabane. 

 These lakes became effaced, quietly, by evaporation and deposit ; 

 others burst bounds and ran off. Thus the Four Masters, and jS'ennius, 

 relate that, a. d. 848, Loch Laeigh, in Mayo, " migrated," and " ran 

 off into the sea." Again, a.d. 1054, Lough Syorun, in Cavan, "mi- 

 grated in the end of the night of the Festival of Michael, and went 

 into the river Feabail, which was a great wonder to all." Finally, 



