OCR Text |
Show 260 DENUDATION OF THE LAND CHAP. VI. water-spouts would remove all the mould from a very gentle slope ; but when e~- am1. m. ng the steep , turf-covered slopes In Gl en R oy, I was struck with the fact how rarely any such event could have. happened since the Glacial period, as was plain from ~he we 11 -preserv ed State of the three suc.c essive " roads" or lake-margins. But the diffi~ulty in believing that earth in any appreCia~le quantity can be removed from a ge~tly mclined surface, covered with vegetatiOn and nlatted with roots, is renwved through. the agency of worms. For the many castmgs which are thrown up during rain, and those thrown up some little time before hea:y ~ain, flow for a short distance down an Inchne~ surf :a ce. Moreover much of the finest levi-gated earth is washed completely away ~rom the castings. During dry weather castmgs often disintegrate into small rounded pellets, and tLese from their weight often roll down any slope. This is more especially apt. to occur when they are started by the wmd, and probably when started by the touch of an an.i ma1, however small. We shall also . see that a strong wind blows all the castmgs, CrrAP. VI. AIDED BY WORMS. 261 even on a level field, to leeward, whilst they are soft; and in like manner the pellets when they are dry. If the wind blows in nearly the direction of an inclined surface, the flowing down of the castings is much aided. The observations on which these several statements are founded must now be given in some detail. Castings when first ejected are viscid and soft; during rain, at which tin1e worms apparently prefer to eject them, they are still softer ; so that I have sometimes thought that worms must swallow much water at such times. However this may be, rain, even when not very heavy, if long continued, renders recently-ejected castings semi-fluid; and on level ground they then spread out into thin, circular, flat discs, exactly as would so much honey or very soft mortar, with all traces of their vermiform structure lost. This latter fact was sometimes made evident, when a worm had subsequently bored through a flat circular disc of this kind, and heaped up a fresh vermiform mass in the centre. These flat subsided discs have been repeatedly seen by |