Geology and Geography. S75 



which nothing could be more splendid. The map in the present 

 case adopted is Arrowsmith's, and it had been found necessary 

 to make the geological colouring conform to the gcogriiphicai 

 inaccuracies it containp. As an example of such imperfection?, 

 it was mentioned, that, in Arrowsmith's map, Ben Wee Head, 

 which is due west of Sligo, is placed twenty miles north of th&t 

 parallel. A new map of Ireland is about to appear in London, 

 and which, if it shall be found to agree with the trigonometrical 

 survey maps, it is Mr Griffith's intention to employ. In point- 

 ing out the remarkable features of the country, Mr Griffith 

 dwelt on the position of the mountain groups, which, except 

 when limestone occurs on the coast, form the margin of the 

 island, and inclose a vast plain which is chiefly of limestone, 

 Oxvino- to this arrangement the river courses are short, except 

 that of the Shannon, which is 140 miles long, and falls 80 feet 

 the first 20 miles, and only 80 the remaining 120 miles. Oa 

 the oreat plain of the interior there occur extensive ridges of 

 gravel, called "escars," which are sometimes 100 feet in height, 

 and which, though nearly constant in direction when considered 

 in small spaces, are variable when the comparison extends to 

 spaces of greater magnitude. They run for ten, twenty, (5r 

 even thirty miles, and formerly the roads were frequently coh- 

 structcd on their summits. In the county of Mayo, the gravel 

 hills run east and west, whereas to the north they run north ami 

 south. According to Mr Griffith, the great bogs were formed 

 in hollows, in which the water w^s dammed up by tlfese gravel 

 hills. Under the bogs very extensive and deep deposits of n;ari 

 occur underlaid by clay and gravel. The marl is in some vst- 

 stances forty feet in thickness. The colours adopted by IM" 

 Griffith in the construction of h.is map are chiefly those used by 

 Mr Greenough. Confining himself, on this occasion, to t!ie 

 stratified rocks, Mr Griffith first considered the gneiss and slate 

 districts, and stated his opinion that the primary group of the 

 north-west and west of Ireland corresponds to a similar grcu^i 

 in the Grampians of Scotland; while the Down slaty group is 

 probably connected with the rocks of Dumfriesshire, &c. Xo 

 relation has hitherto been ascertained to exist between the Wick- 

 low series and any group on the opposite side of the Channei, 

 The general direction of the stratillcation to llie noith of Ireland 



