704 J'ROTECTIOX AGAINST DISEASES. 



formerly tlie case when the shafts of the smelting furnaces 

 were open, and the furnaces themselves much more numerous 

 than at present. Dudley Park is exposed on the east to the 

 acid fumes of smelting furnaces, and yet ash, poplar, and 

 sjxamore trees are growing there fairly well with elder, 

 hawthorn and hazel undergrowth, while beech appears on the 

 western slopes of the park, that are exposed to open 

 country where there are ^lo furnaces. Grass grows well 

 enough in the Black Country, and there can he no reason 

 why the large extent of uneven grassy land near Bilston 

 (about 14,000 acres), where the coalfields have been worked 

 out, the soil being weathered shale, should not be planted 

 with trees, instead of remaining, as it is at present, a dreary 

 waste. It is said that to level this land would cost £100 per 

 acre, but no levelling would be necessary, if it were to be 

 planted up with trees, which grow well enough on similar 

 land in Belgium. 



There are works at Bilston for galvanising iron, and the 

 molten zinc in which the sheets of iron are plunged is covered 

 with chloride of ammonium to jjrevent its oxidising. The 

 fumes given off during the process are said to kill all leaves of. 

 trees near the works by June every year, but these fun)es 

 probably extend only for a short distance from the works. 



Since 1903 planting has been undertaken in the Black 

 Country under the auspices of the Midland Eeafforesting 

 Association. (Vide Figs. 297, 298). 



r. Age of Trees. 



"Woods suffer from acid fumes at all ages, but poles 15 — 30 

 years old appear to suffer most. 



(I. Locality. 



The influence of the locality makes itself felt chiefly by the 

 direction of the prevailing winds which bring the fumes 

 towards the trees. 



The Belgian Commission mentions 2,000 meters as the 

 greatest distance from chemical works, in the direction of the 

 prevailing winds, at which damage was observed. In certain 

 cases, however, woods have been injured at distances of 



