SiGERSON — On. the Physical Geography of Ireland. 7 



but a very unjustifiable credulity in their successors, who could sup- 

 pose the first discovery of them to be their first rise. . . But as it 

 appears to be almost a certainty, that (with a very few exceptions) 

 rivers and lakes are nearly coeval with the creation, the reader will, 

 I hope, excuse my taking no further notice of this part of our history." 



Now, I confess, that on first giving attention to these records iden- 

 tical speculations presented themselves as ingenious and satisfactory ; 

 they accounted for everything by explaining all away. Fortunately, 

 the language of the annals is not ambiguous, and it is impossible not 

 to perceive that when the word eruption is employed, something is 

 meant quite different from inundation, a term also used. Again, 

 O'Halloran's hypothesis falls before the fact that those lakes and rivers 

 which, from their position and size, were most readibly discoverable, 

 are not mentioned first, some of them not at all. Of two neighbouring 

 lakes, the larger and more accessible may be left unnoticed, whilst the 

 eruption of the smaller is chronicled. Finally, if his hypothesis were 

 valid, it would follow from the data given, that Ireland was first co- 

 lonized in that part which is now the county Mayo, that the newcomers 

 soon discovered Lough Conn and Lough Mask, but never found Lough 

 Corrib ; that they afterwards proceeded to prospect a few small lakes 

 in what is now the county Monaghan, without ever having observed 

 the Shannon's spreading sea. 



It may, perhaps, be possible to account for the formation of a few 

 lakes by some of the changes operated on the face of the country, by 

 the progress of colonization. Here there is repeated mention of the 

 clearing away of forests. Fire as well as the axe was doubtless em- 

 ployed in this work, and the charred remnants may occasionally have 

 helped to block the path of flowing waters and bar the drainage of 

 small areas. The removal of a forest from a given space itself removes 

 a drainage organ of no inconsiderable power. Hales found that a sun- 

 flower with a leaf surface of thirty -nine square feet exhaled twenty- 

 two ounces of water in the twenty-four hours ; Knop, that a plant of 

 maize, in three months and a half, exhaled thirty-six times its own 

 weight of water. When we consider how extensive is the leaf-surface 

 of trees, and how great the transpiration, a forest might almost be re- 

 garded as an engine for di'aining up a river from the earth and dissi- 

 pating its'^waters through the air in the form of insensible vapour. 

 Thence, it descends again in showers. The first effect of felling forests 

 in Ireland, under the circumstances of the period alluded to, might 

 have been therefore the formation of pools, streams, and lakelets — the 

 secondary effects would be shown in their gradual diying up, when 

 the land was exposed to the full rays of the sun. 



But, although we may possibly account for the formation of some 

 water courses and lakes in this way, we do not account for the emphatic 

 employment of the term eruption, nor for the successive pheno- 

 mena chronicled. It is to be noted also, that the clearances are not 

 coincident in space, nor always in time, with the formation of lakes 

 and rivers. 



