BY T. W. EDGEWORTH DAVID. 497 



the coal basin. This supposition would, if correct, explain the 

 fact that kerosene shale is chiefly restricted to the edges of the 

 coal basin. \Vind blowing ofi* the hills would be apt to carry with it 

 spores from cryptoganiic plants, and deposit thero over the swampy 

 flats of the coal basin, much in the same way that the pollen from 

 the catkins of the fir is blown over the pine forests and lakes of 

 Scotland, Scandinavia, and Canada, as described by Dr. John 

 Davy."^ Such deposits, even at the present day, frequently attain 

 a thickness of half an inch. Where the pollen shower falls on 

 earth it soon becomes mixed with the decayed vegetation and 

 earthy imparities, but where it falls on the surface of lakes it 

 floats for a while, then becomes water-logged and sinks to the 

 bottom, where it would form a thin layer of inflammable material. 

 If little or no muddy sediment were received into the lake, such 

 an accumulation might go on from year to year until it had 

 acquired a considerable thickness, and such light material as leaves 

 of trees and needles of the fir would be liable to become interbedded 

 with this deposit. Such a deposit, however, would not be uniformly 

 ]mre, as every shower of rain would be sure to wash in a little 

 sediment round the margin of the lake, and so render the pollen 

 sheet clayey along such areas of sedimentation. Somewhat 

 analogous to these pollen showers is the spore dust from tree-ferns, 

 which is described by R. M. Johnstonf as so filling the air at 

 certain seasons in the fern-tree gullies of Tasmania, as to afi"ect 

 travellers with fits of sneezing while passing through such belts of 

 spore-laden atmosphere. 



Phenomena somewhat analogous to those of the pollen and 

 spore showers would be likely to have obtained on a grander 

 scale during the Permo-Carboniferous Period in Australia. Here 

 and there around the margins of the low-lying swampy flats in 

 which the coal was being found there would be likely to be 

 shallow lakes devoid of vegetation, so that although the supposed 



* Proc. Eoy. Soc. Edinburgh, Vol. IV. p. 157 (1859). The author is in- 

 debted to Professor A. H. Green's Geology, Part I. p. 184 (1882) for this 

 reference. 



t Geology of Tasmania, by R. M. Johnston, F.L.S., &c., 1888, p. 138. 

 32 



