20 Proceedings of the Royal Irish Academy. 



times. Trithin three huiLdred years, the "w^aters of the Swilly and 

 Poyle ^vere connected by it. What I would here add is, that in 

 remote times the river Foyle itseK (going partly or wholly by the 

 ■western side of Derry Hill) has passed through this valley into Lough 

 Swilly. Though farther geological investigation* is required to de- 

 termine the acciu'acy of this supposition, it receives support from the 

 physical appearance of the district, and from the gradual drying up of 

 the valley-channel, when the Poyle found another vent. The most 

 ancient map of Ireland shows only one lough (Swilly) in this district, 

 and the ancient chi'onicles do not notice the existence of that gTeat 

 sheet, now known, on the map as Lough Foyle. They did, indeed, 

 make use of the name, but it was applied to a large lake (now obli- 

 terated) which I proved to have spread out its waters between Strabane 

 and Derry. The river which passes through the alluvial deposits that 

 filled the lake, like a current through a frozen sea, still retains the 

 name of Lough Foyle, and when swollen by floods resumes some of its 

 former sway over the submerged flats. 



Passing to another question, the eruption of Lou^h IS'eagh, there 

 is here also to be found geological evidence in support of the 

 statement of our ancient chronicles, which asserted that it was formed 

 suddenly and (to them) mysteriously. "Lough IN'eagh," Captain 

 Portlock remarks, " is itself apparently the result of a great crack or 

 subsidence of the strata." 



It only remains to say that evidences of upheaval are visible 

 in the deposits reaching up the Dublin Mountains, in the levels 

 along the Lee above the^City of Cork, and southwards in the raised 

 beaches of Kerry ; whilst proof of subsidence is found in the fact, 

 communicated by Professor W. K. Sullivan, that ancient bog and 

 forest stretch out beneath the sea, ofi' the coast of Waterford. 



The more the question is investigated, therefore, the more do 

 proofs abound to demonstrtite that, in ancient times, this island was 



* Having established, in a Paper entitled " Discovery of Fish Remains in the alluvial 

 clay of the Paver Foyle, &c.," the insulation of Innishuwen, I pointed out that tlie 

 eschuatnient map of 1609 showed another channel connecting the Foyle and Swilly, 

 running from " Cargan " (now Carrii,'an) to " Kihnaeatrem Castle," and that Malin was 

 insulated. This was but briefly noticed, as corroborative evidence was not then accessi- 

 ble. Since that time I have gone over the locality, and found confirmation of the map 

 in the conformation and character of the soil. Tlie former insulation of Malin is very 

 evident, though at present the water channel is occupied by a great bog. The substratum, 

 however, is either potter's clay or gravel. The ancient channel or strait ran between 

 Culdaffand Malin town, a distance of about three miles in a direct line, being somewhat 

 shorter than the isthmus at Pennyburn. Interspersing the vast bog which i'.as now 

 largely occupied its place, are oases of clay land, formerly islands, and about midway 

 on ihe moor is a village whose name, Aughnaclea, signifying "Ford of Hurdles," 

 indicates the former presence of water. As the channel must have existed in 1609, when 

 tile escheatment map was made, aud as a great b.ig has since been formed, we have here 

 desirable and valuable data for arriving at the rate of bog growth. Plainly this great bog 

 cannot be manv cenluries old. — Trdc Proc. K. Irish Acad., Vol. I., Ser. 2, Science, 

 •p. 212. 



