56 FIRST FORMS OF VEGETATION. 
the surface by the sunshine and rain, blackened. 
here and there by dissolving wreaths of snow 
which lie upon them through all the summer 
months, and gradually decomposing underneath 
into black vegetable mould. The shoulders, 
ridges, and elevated plateaus of all the Highland 
mountains are covered. with huge luxuriant masses 
of the woolly-fringe moss 1 (Trichostomum lanugi- 
nosum), growing continuously over whole acres of 
ground, and banishing every other plant from its 
domains. Mountain peat, which is of a dry, friable 
nature, is formed almost exclusively by the decay 
of this moss. It seems intended by nature to. 
serve as a covering to the soil—in the absence of 
grass and heather—as it is found most luxuriantly 
and in the greatest profusion in spots considerably 
above the heather line, and even above the point 
where grass ceases to be a social plant, and occurs 
only in scattered tufts here and there. In these 
bleak and desolate spots, it sometimes furnishes 
materials for an extemporaneous couch to the be- 
lated traveller, compelled to sleep in the shade of 
a rock on the hills ; although care must be taken 
in arranging the couch to place the dry surface 
uniformly uppermost, otherwise the wet decom- 
posed portions will here and there obtrude, and 
render the repose of the tenant exceedingly un- 
1 See Frontispiece. ° 
