132 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



understood when it is remembered that till consists simply of 

 crushed bed-rock, and that its character must change with that 

 of the bed-rock of a district. Thus, in regions occupied by 

 Old Red Sandstone, the till is red and more or less arenaceous, 

 and not infrequently yields a fertile soil. Where, on the other 

 hand, the dominant rocks are white and grey sandstones, and 

 black argillaceous shales, together with fire-clay, coals, iron- 

 stones, and limestones, the till is greyish-blue or leaden-coloured, 

 and usually very tenacious — yielding a most ungrateful soil. 

 In some places, again, the till contains a large admixture of 

 crushed basalt or other igneous rock, and, when not too im- 

 permeable, such a till is overlaid with soil of good quality. 

 Chalky boulder-clay, composed chiefly of pulverised chalk, 

 yields a clay-soil, from which, in most cases, the calcareous 

 constituents have been in large measure removed. Upon the 

 whole, the best soils met with in districts covered with till are 

 brown and red-coloured — forming, as these frequently do, strong 

 loams rather than clays. 



Stoneless Clays. — These clays are also of glacial origin, but 

 have been accumulated in water. Most of them were laid 

 down in the sea at a time when the land was partially sub- 

 merged, and they are therefore confined to low-lying maritime 

 districts. Good examples are met with in the lower reaches 

 of the great valleys of Central Scotland, where they form a 

 considerable proportion of the carse-lands of the Tay, the Forth, 

 and the Clyde. In composition these clays do not differ from 

 true till. Like the till, they consist of unweathered rock-material. 

 They represent the fine mud, etc., swept into our estuaries by 

 turbid rivers escaping from glaciers, too short a time having 

 elapsed before they settled down on the sea-floor to allow of 

 much chemical alteration. Except when they alternate in thin 

 layers with beds of sand, they naturally form exceedingly 

 tenacious clay-soils. When interbedded sand is present, the 

 resulting soil is less ungrateful. 



In the case of both the stony and stoneless clays of glacial 

 origin, it is obvious that deep ploughing ought to be avoided. 

 The soil-caps covering both are alike thin, and have taken a 

 long time to form. Deep ploughing, therefore, simply buries 

 the soil and subsoil below a raw clay, in which seed is just 

 as unlikely to germinate as it would on the bare surface of 

 any unweathered bed-rock. 



