Correspondence — J. Parldnson. 191 



•rapid disintegration which the surface is undergoing it is roughened 

 rather than glazed. The largest cavity is in a block 6 by 4 by 

 4 feet, which is hollowed almost to a shell. The cavity is four feet 

 long, three feet deep, and two feet high, and has four apertures 

 varying from a foot to eighteen inches in diameter, and corresponding 



Fig. 2. — Cavity in a block of very coarse granite, 6x4x4 feet. The cavity is 4 feet 

 long, 3 feet deep, and 2 feet high, and has four apertures varying from a foot 

 to 18 inches in diameter, one on each side of block. 



in position to the centre points of the four sides of the original 

 block. The lip of the apertures is exceedingly sharp, and the solid 

 angle is certainly not greater than 30°. No incrustation was seen 

 on the walls of this cavity, but on the floor is a sprinkling of the 

 finer disintegration products of the granite which abundantly litter 

 the surrounding area. 



From this brief description it will be seen that the former type of 

 Antarctic granite cavities closely resembles in shape and in superficial 

 glaze the cavities described in Corsica and in Madagascar. As in 

 Corsica, many saucer-like depressions and a few potholes were 

 observed, and seem to mark stages in the development of the com- 

 pleted cavities. Internal incrustations do not seem to be recorded, 

 but Mr. Baron mentions a " white powder alkaline to the taste " as 

 occurring in the hollowed blocks of Madagascar. 



Sidney Sussex College, Cambridge. H. T. Ferrar. 



February IWi, 1905. 



THE PROSPECTORS' PAN. 



Sir, — May I be allowed to point out the advantages to be derived 

 by the use of the prospector's pan as an aid to research in geology ? 

 Everyone interested in the subject is, of course, aware that minerals 

 of economic importance may be traced to their original sites by 

 successive pannings taken from the alluvium of a stream at points 

 successively nearer to the source, due attention being paid to the 

 incoming of tributaries ; but the method is not in common use by 

 the geologist. 



The gold pan treats some 25 lbs. of medium gravel, containing 

 small boulders, at one time, and the operation of panning can of 

 course be stopped at any stage desired so as to include or exclude 

 such minerals as tourmaline and hornblende, I would suggest 

 that for investigations into the mineralogical composition of glacial 

 deposits and the more compacted sediments this method of pannino" 

 might be tried. In dealing with a hard rock, pounding in a mortar 



