Ch. XXIY.] 



COAL — EAIN-PRIN-TS. 



381 



Fi-. 495. 



Fig. 496. 



Fig. 495. Carboniferous rain-prints with worm-tracks {a, I) on green shale, from Cape 



Breton, Nova Scotia. Natural size. 



Fig. 496. Casts of rain-prints on a portion of the same slab, fig 495, seen on the under 



side of an incumbent layer of arenaceous shale. Natural size. 



The arrow represents the supposed direction of the shower. 



observable some small ridges as at a, which stand out in relief, and 

 afford evidence of cracks formed by the shrinkage of subjacent clay, on 



Fig. 497. 



fig. 497. Casts of carboniferous rain-prints and shrinkago-cracks (a) on the under 

 side of a layer of sandstone, Cape Breton, Nova Scotia. Natural size. 



which rain had fallen. Many of the associated sandstones are ripple- 

 marked. 



The great humidity of the climate of the coal period had been pre- 

 viously infeiTed from the nature of its vegetation and the continuity of 

 its forests for hundreds of miles ; but it is satisfactory to have at length 

 obtained such positive proofs of showers of rain, the drops of which 

 resembled in their average size those which now fall from the clouds. 

 From such data we may presume that the atmosphere of the carbo- 

 niferous period corresponded in density with that now investing the 

 globe, and that different currents of air varied then as now in tempera- 



