THE INFLUENCE OF GEOLOGY ON HORTICULTURE. 



395 



4. Sandy loams. 



5. Sands. 



6. Marly soils. 



7. Calcareous soils. 



8. Vegetable moulds. 



Technically " soil " may be defined as that portion of the earth's crust 

 which man breaks up in the cultivation of crops, while subsoil is the 

 material lying below the soil turned up by the spade or plough, into 

 which the roots of plants penetrate, and extending down to the solid 

 rock, whether it be hard as granite or soft as clay (fig. 73). The 

 character of the soil is largely dependent on the subsoil. 



The earthy matter of soils has been produced by the gradual 

 crumbling down of previously existing rocks, through the action of 

 water, frost, change of temperature, and vegetation. The decay of 

 vegetation itself produces acids which decompose rock. 



The work of earthworms is also of importance in mixing, grinding 

 up the soil, and letting air into it. 



The influence of geology on plants is modified by altitude, rainfall, 

 natural drainage, proximity to the sea, Sec. ; thus we have a special flora 

 on high mountains, on marshy land, and in proximity to the sea, to a 

 considerable extent independent of the rock beneath. 



Table I. — Influence of Rainfall and Altitude upon Vegetation. 

 A Section from Snowdon to Essex. 

 By Professor Primrose McConnell, in his "Elements of Agricultural Geology." 





lerionetli. 



ontL'omery. 



liropsliire. 



Worcester. 



Warwick. 



J 



| 



Bedford. 



Herts. 



Essex. 









ai 







o 









Rainfall : inches per 





















annum, upproxiiu. . 



100 



95 



45 



35 



30 



27 



25 



22 



20 



Height above sea in 





















feet, average . 



900 



700 



400 



:too 



270 



250 



230 



220 



200 



Cora acreage per cent. 



111 



203 



22-4 



262 



25-7 



29-8 



42-0 



42-3 



46-3 



Grass acreage per cent. 



75-9 



63-8 



58-2 



52-9 



56-4 



52-8 



31-4 



29-7 



242 







-** 















Geological formation . 



Primary rocks 



Secondary rocks 



Tertiary 

 rocks 



Table II. — Influence of Underlying Rock on Surface Vegetation. 

 Prepared by the late Professor James Bucknian. 



Underlying rock. 



Apple. 



Pear. 



Oak. 



Elm. 



Lieeeh. 



Pine. 



Old red sandstone . 



15 



8 



8 



10 



0 



1 



Lias clay .... 



10 



3 



5 



10 



0 



1 



New red sandstone marl . 



8 



0 



7 



12 



0 



2 



Oxford clay 



6 



0 



10 



8 



0 



1 



Oolitic limestone 



2 



0 



1 



4 



10 



5 



Chalk .... 



2 



: 



2 



4 



8 



5 



Gault clay 



4 





(') 



6 



0 



0 



Greensand 



3 





3 



7 



0 



3 



Mountain limestone. 



; 1 



_L 



2 



2 



3 



1 



* The figures represent the relative frequency of the trees growing upon the different formations. 



