ORIGIN AND DEVELOPMENT OF HEATHER MOORLAND. 121 



tion at the expense of another. Wind-borne sand may also 

 overwhelm forests or other vegetation, and lead to the develop- 

 ment of heath or other sand types. 



One of the objects of the Scottish botanical survey is to ascer- 

 tain the extent of our primeval forest, hence the importance of 

 Graebner's observations. The origin of the heather moorlands 

 in Scotland has a very direct bearing on the afforestation of our 

 moors, a prominent item in the work of the Scottish Arboricultural 

 and kindred societies. In many instances it has been proved that, 

 with proper treatment, our moors may be converted into forests of 

 Coniferse. This would indicate that the soil of our moors, especi- 

 ally the drier types of heather moor, is not yet too exhausted to 

 carry forests. The extensive and successful conversion of heather 

 moor into farmland in earlier times also points this way. At 

 present we consider that a large proportion of the heather moor- 

 land in Scotland has been derived from ancient forest, but in the 

 Pennine chain in England there is less evidence of this. The 

 heath vegetation is the result of a moist climate, which favours 

 the accumulation of raw humus cut off from the true soil by a 

 moor-pan or an impervious layer of fine clay. Natural poverty of 

 soil in itself is only responsible in a few cases, such as the thin, 

 stunted heaths of saTid-dunes. Other causes of conversion are the 

 influence of man through sheep-grazing and drainage, and, in a 

 less degree, through the favouring of heather and its associates by 

 the regular burning of grouse-moors. 



