Geological Societi/ of Ireland for 1847. 313 



ment of the particles of matter, taking place at different times, with- 

 out the bedded or laminated structure of the original rock being lost, 

 in consequence of actual fusion by contact with the adjacent molten 

 mass of granite, is one of no small geological importance when the 

 laminated crystalline rocks, forming whole regions in some parts 

 of the world, are under consideration. Prof. Oldham points out 

 that Mr Weaver had, many years since, remarked, respecting the 

 rocks of this part of Ireland, that "the character of this andalusite 

 is altered by a more or less intimate mixture of mica." 



Prof. Allman read a paper on erratic blocks of greenstone, found 

 scattered over carboniferous slate, in the vicinity of Bandon, county 

 Cork. As is well known, Ireland is, in many districts, covered by 

 gravels and sands, occasionally mingled with blocks of large rocks, all 

 of a comparatively recent geological date. If these be sea-borne, we 

 should require the submergence of the land, and generally with its 

 present physical features, to a depth of more than 1000 feet beneath 

 the present level of its shores. The mode in which thousands of large 

 blocks of gi'anite are scattered over the flanks of mountains and over 

 districts, facing great valleys, in the counties of Wicklow and Wex- 

 ford, are often highly instructive. This " drift," as it is frequently 

 termed, most materially influences the agricultural character of large 

 districts in Ireland. 



The communication of Prof. Allman was followed by another from 

 Mr Mallet, in which the latter endeavours to shew that the trans- 

 port of boulders or erratic blocks may be accounted for by the slow, 

 or occasionally rapid movement of semi-fluid masses of mud, sand, 

 gravel and blocks, forming the bed of the sea (and either of sufficient 

 depth and mass alone, or resting upon a base of rock or other mate- 

 rials of very moderate slope), combined with the sorting and trans- 

 porting power of the tidal streams upon the finer materials of the 

 whole mass. Mr Mallet considers that the mass of a loose sea-bot- 

 tom may be constantly sliding outwards, forming a kind of mud- 

 glacier, as he terms it, the whole reduced to nearly one-third of its 

 weight in air by immersion in water, and moving gradually over 

 slopes of three or four degrees, and even less. In this manner, he 

 observes, we may account for the grooving, furrowing, and scratch- 

 ing, so commonly remarked among these accumulations of gravels 

 and blocks, pebbles and great fragments of rock being held firmly 

 in tlie under part of the moving mass, and grating against the bot- 

 tom. These scratches, now so commonly found on the surface of 

 rocks in the northern parts of the earth, and which may be equally 

 so in the southern, allowing for the difference of area there occu- 

 pied by land, have been long pointed out by Dr Buckland and 

 others in the British islands, and have of late been frequently, as 

 is well known, adduced as evidences of the former existence of gla- 

 ciers upon the districts where such scratches are found. Mr Mallet 



