| OCR Text |
Show 284 DENUDATION OF TIIE LAND. CIIAP. Vl. leeward side, from the upper part having curled over the lower part. During one unusually heavy south-west gale with torrents of rain, many castings were wholly blown to leeward, so that the mouths of the burrows were left naked and exposed on the windward side. Recent castings naturally flow clown an inclined surface. but on a grassy fi eld, which sloped between 10° and 15°, several were found after a heavy gale blown up the slope. This likewise occurred on another occasion on a part of my lawn where the slope was somewhat less. On a third occasion, the castings on the steep, grass-covered sides of a valley, down which a gale had blown, were directed obliquely instead of straight down the slope ; and this was obviously due to the combined action of the wind and gravity. Four castings on my lawn, where the downward inclination was 0° 45', l 0 , 3° and 3° 30' (mean 2° 45') towards the north-east, after a heavy south-west gale with rain, were divided across the mouths of the burrows and weighed in the manner formerly described. The mean weight of the earth below the mouths of burrows and to leeward, was to that CHAP. VI. CASTINGS DLOWN TO LEEWARD. 285 above the mouths and on the windward side as 2! to l; whereas we have seen that with ::)everal castings which had flow ed down f::llopes having a mean inclination of 9° 26', and with three castings where the inclination was above 12°, the proportional weight of the earth below to that above the burrows was as only 2 to 1. These several cases show how efficiently gales of wind accompanied by rain act in displacing recently-ejected castings. We may therefore conclude that even a moderately strong wind will produce some slight effect on them. Dry and indurated castings, after their disintegration into small fragments or pellets, are sometimes, probably often, blown by a strong wind to leeward. This was observed on four occasions, but I did not sufficiently attend to this point. One old casting on a gently sloping bank was blown quite away by a Rtrong south-west wind. Dr. King believes that the wind removes the greater part of the old crumbling castings near Nice. Several old castings on my lawn were marked with pins and protected from any disturbance. They were examined after an interval of 10 |
