A DUST-FALL IN THE SOUTH-WEST OF ENGLAND 89 
It has been suggested by Mr. J. J. H. Teall, director of 
the Geological Survey, that the question of the origin 
of dust floats might be elucidated if the samples obtained 
were found to contain free aluminium hydroxide. The 
reason for this suggestion is that laterite, a decomposition 
product of the felspars, is an aluminium hydroxide, though 
always mixed with more or less silica. It is believed that 
this ^ type of decomposition occurs only in tropical 
regions, and consequently if uncombined alumina in the 
dust could be detected the evidence of a tropical origin 
might be established. Professor T. E. Thorpe has made 
some experiments in this direction on the two samples of 
dust he has studied, and he remarks that “ the results are 
not conclusive, but so far as they go they point to there 
being no uncombined alumina in the samples.” ’ 
7 Nature, vol. Ixviii. p. 223. 
