266 G. H. Kinahan — On the Growth of Soil. 



for similar reasons horses are harder on grass land than either sheep 

 or cows. It may be said that on pasture land the vegetable products 

 are not allowed to decay. In one sense they are not, but if they are 

 eaten off by the cattle they are returned again to the surface, their 

 fertility being increased from their having been used as animal food. 



In a comparison between meadow and pasture land, the "hand 

 joined in hand" work of vegetation and of the earthworm appears 

 conspicuous. Examine a meadow field after the hay is cut, and the 

 worm-works will be found to be few and far between, but if the 

 after-grass is allowed to rot on the land, and during that process the 

 field is examined, worms will be found working everywhere among 

 the decaying vegetable matter ; and in the pasture-land there will 

 be a hundred worms for every one in the meadow-land, the largest 

 portion being found under and associated with the decayed vegetable 

 matter in the droppings from the cattle. 



Although, as previously stated, Darwin seems to infer that the 

 thickness of the mould does not increase upward, that is, its height 

 is not added to by an increase from the decay of the vegetable 

 matter, although the full thickness may be increased by the earth- 

 worms working up part of the subsoil ; yet in no instance is a fact 

 put forward that would favour such a supposition. But on the 

 other hand, facts may be stated which apparently would prove that 

 it does increase upwards. To give a homely instance. Previous to 

 the introduction of wire railings, the usual fencing in parks and 

 pleasure grounds were iron hurdles with double knee-shaped legs. 

 When the hurdles were placed in position, they were forced down 

 till the knees were on a level with the surface of the ground, but in 

 a few years the knees were not only covered, but a greater or less 

 thickness of soil had grown over them. A stone, a piece of crockery, 

 or some such substance, although not probable, might possibly sink 

 bodily with the whole surface of the ground as the earth was exca- 

 vated from below by the earthworms, and carried up by the same 

 agents to be placed on the surface ; but this could scarcely be the 

 case with a railing half a mile or more long, and yet over every 

 knee I have observed an equal growth of mould. But if there is 

 an increase upwards in the thickness of the soil due to vegetable 

 decay, it would be natural to expect that each knee of the different 

 hurdles should be gradually and at the same time covered. 



Darwin brings forward a startling fact in favour of the burrowing 

 powers of the earthworm, in his quotation from Mr. W. Lindsay 

 Carnegie's letter, however that may possibly be an exceptional 

 case ; for in the alluvial earth, forming some of the flats adjoining 

 rivers in Ireland, such as that along the Little Brusna, the river 

 which divides Tipperary from the King's County, I have, during the 

 arterial drainage works in operation nearly twenty years ago, 

 observed the burrows of the earthworms at great depths, but usually 

 they seem incaj)able of penetrating into the ordinary sub-soils that 

 occur in Ireland. The gravelly sub-soils formed by the Esker or 

 post-drift gravels ought to be soft enough for them to work into, 

 yet I never remember remarking a worm-burrow in them. The 



