242 On the Alpine Glacier, Iceberg, £No. 159. 



A block of mica schist, weighing upwards of eight tons, lies on the 

 top of the Pentland hills, 1000 feet above the sea, 50 miles from the 

 nearest mountains of mica schist. 



When loose, round, or angular masses of rock are seen on the sur- 

 face, or imbedded in loam, clay or gravel, the nature of the rock and 

 that of the subjacent and adjacent rocks should be compared. If 

 they are similar, it will be difficult to prove the masses true boulders. 

 If different, the bearing and distance of the nearest similar rocks should 

 be ascertained, and the nature of the intervening ground described whe- 

 ther intersected by valley, hill or stream, &c. In all cases, specimens 

 about two inches square or more of the blocks, the adjacent and subja- 

 cent rocks, and of those from which they are supposed to have been 

 derived, should be broken off, and wrapped up in strong paper and 

 carefully marked. 



If it be certain that they are boulders, or erratic blocks, and not " in 

 sitd" their size and shape and number should be described, drawings 

 made, the arrangement and longitudinal direction of the blocks, their 

 bearings by compass, the height above the sea if possible, a description 

 of the physical features of the locality and surrounding country. 

 When circles of blocks are found round the tops of hills or other 

 projecting points of the surface, care should be taken not to confound 

 the old cairn-like mounds, circular burial places, old sheepfolds, remains 

 of forts, or other old enclosures scattered over India, for the circles 

 called u perched blocks." 



The old inhabitants and watchmen (Taliaries) of the nearest village, 

 should be carefully questioned on such points. 



When erratic blocks can be traced to the parent rocks, it should be 

 carefully noted whether they gradually increase in size as the rocks 

 whence they were transported are approached. 



Gravels, Clays, and Sands of the Boulder formation. The 

 boulder formations of England, (called " Till" in Scotland,) of 

 the north of Europe and America, and also that in the opposite he- 

 misphere, are — 1st, characterized, principally, by their generally unstra- 

 tified character ; 2nd, by imbedding both large and small, angular 

 and rounded fragments of rocks of all ages in juxta- position, con- 

 fusedly jumbled together without reference to the laws of gravitation 



