594 C. EICKETTS ON THE EEEATICS IN THE 



also occur in the sandy Boulder-clay which immediately overlies 

 these sands and gravels. Mr. A. Strahan, P.Gr.S., of H.M. Geolo- 

 gical Survey, informs me that he has observed them under similar 

 conditions in other places. 



It is more particularly desired to direct attention to the occurrence 

 of other boulders which frequently bear evidence of glacier-action, 

 and have also been exposed to other influences before they were 

 floated away and dropped into the clay. Some, of granite, are 

 weathered all over, their entire surface being roughened and so far 

 disintegrated that fragments can be broken oif by the fingers *; 

 others in the same state have also had a portion split off. Some, 

 having their surfaces glaciated, crumble into fragments by slight 

 pressure ; whilst others cannot be removed without separating into 

 their component crystalline particles, though when in situ each 

 granule retains its relative position, and a careful removal of the 

 clay may even show their surfaces to be smoothed and polished. 



A somewhat similar kind of weathering is often observed in 

 various kinds of volcanic rock. In some it peels off in concentric 

 laminse ; where this disintegration has not penetrated the whole 

 mass, the central nucleus remains solid and unaffected. Examples 

 of a different kind are frequent in which the mass is disintegrated 

 throughout, being easily crushed or broken and the granules sepa- 

 rated. The striae formed previous to weathering in a few cases 

 remain visible. 



Mr. G. H. Kinahan, of H.M. Geological Survey of Ireland, has 

 informed me that blocks of disintegrated granite are frequent in the 

 glacial deposits, especially those of "Wicklow and south-east Wex- 

 ford, being more prevalent in moraine-drift than in the Boulder- 

 clay. There are granite boulders, imbedded in moraine accumu- 

 lations, near Shap, Westmoreland, which have become disintegrated 

 in various degrees, and to an extent as great as those occurring in 

 the Boulder-clay of Cheshire, whereas at the present time the Shap 

 granite, both- in the well-known blocks and in situ, weathers only 

 on the exterior. 



What Mr. iKinahan states respecting the granite boulders of Co. 

 Wicklow is equally applicable to some of volcanic origin in the 

 glacial deposits of Co. Antrim, where they occur in every stage of 

 disintegration, but modified according to their structure. Examples 

 are met with in moraine- and esker-mounds, and in the Boulder- 

 clay, exactly corresponding with some in the Boulder-clay of 

 Cheshire. 



Rocks of various kinds are coated with a powder, derived from 

 their disintegration, generally of a light-green colour, having mixed 

 with it minute fragments of the same. In some, the general sur- 

 face of which affords proof of glacial erosion, channels or hollows 

 have been formed subsequently, these being filled with similar 

 disintegrated materials. In other instances the weathering has so 



* The condition of these granite blocks coincides with the account given of 

 some in Spitzbergen and Sweden, " spht up whilst in situ by the action of the 

 frost " (' Arctic Voyages of Prof. Nordenskiold,' by Alex. Leslie, p. 233). 



