DR. ANGUS SMITH ON PEAT. 287 



to the extent, in some places, of about one tenth of the 

 dry matter of the peat. The supply of inorganic matter 

 must be brought by water ; and accordingly we find all 

 peat-bogs which grow to a great depth to be in the midst 

 of a very abundant supply. 



Frequently they receive the drainage from a hill, so that 

 all the inorganic matter washed down seems to give the peat 

 the first choice. The organic matter must have its supply 

 of nitrogen, and the abundant rain of the peaty districts 

 never fails to contain some ammonia or some nitric acid. 



Peat, then, grows where water is constantly bringing it 

 food ; and the inorganic matter is easily got even in soft- 

 water districts. One grain of salts in 100,000 would be 

 70 tons per annum on 1000 acres, with 70 in. of rainfall, 

 and enough to grow 700 tons of dry peat or 3500 of wet 

 peat. I have no experience of peat on soils with hard 

 water. 



If the supply of water is small, there is a small supply 

 of peat ; and this we see on places where there is no stream 

 from above ; but it sometimes happens that there is a con- 

 siderable amount of peat on land which occupies the upper 

 part of a rising ground, having no supply of water from 

 a distance at least : in this case there may be from throe 

 to four feet — as an instance, at the stones of Callernish in 

 Lewis, where there is said to have been this thickness. 

 This I suppose to depend on the capillary attraction, as 

 well as on the existence of broken ground or fine earth or 

 very soluble rocks, When it reaches a height not man- 

 ageable by capillary attraction, the peat, I believe, almost 

 entirely ceases to grow, being fed only a little by the rain, 

 or in some places by spray. 



The bogs of Ireland are said to rise as much as 40 feet, 

 sloping down very slightly on all sides, and occupying a 

 great plain. The distance necessary for the water to run 

 facilitates the diffusion of salts. 



