AFFORESTATION OF PIT MOUNDS 69 
did not look very promising for tree growth. A shovelful 
of good soil put in round the roots at the time of planting 
greatly assisted the growth of the young trees at the start. 
Mr. Cadell believes that in many districts pit banks, especi- 
ally those at abandoned mines where there is neither smoke 
nor mischievous people to injure the trees, may be planted 
with a view to profit. Mining districts are usually provided 
with railways, and furnish a good market for any timber 
that is grown locally. 
The immense shale banks around the oil works in West 
Lothian and other districts are difficult to plant. If iron 
pyrites is present, the sulphuric acid formed when the shale 
is decomposed prevents the growth of any vegetation. Mr. 
James Whitton instances shale bings forty or fifty years old 
at Nitshill in Renfrewshire on which not even a blade of 
grass has appeared. Some of the oil shale, however, sup- 
ports plant growth fairly well, as is evident near Linlithgow, 
where Mr. Cadell has noticed the appearance of natural 
vegetation on abandoned bings. The latter might be planted 
with grey alder, black Italian poplar, etc. It must not be 
forgotten that the fumes from shale works are deleterious to 
the growth of trees, the effect being especially grave when 
sulphuric acid required for refining is manufactured at the 
works (8). 
On an extensive slag heap at Quaregnon, in Belgium, 
planted up in 1891 with Robinia, alder, elm, birch, horn- 
beam, ash, sycamore, horse-chestnut, laburnum, etc., the best 
species appears to have been Robinia, which in eighteen 
years after planting had attained as much as three feet in 
girth. On another large slag heap, planted 25 years, 
hybrid black poplar was also three feet in girth. M. C. 
Leonard, who gives an account of these plantations in 
Annales de Gembloux, Oct. 1909, recommends that, after 
weathering for eight or ten years, a heap should be covered 
first with herbage by sowing seeds of grasses, lucerne, 
sainfoin, ete, and afterwards be planted up with 3- to 
4-year-old transplants of Robinia, birch, grey alder, Prunus 
serotina, sycamore, and Quercus rubra. 
