292 ON THE SOILS AND SUBSOILS 



careful cultivation of Scotch firs, Norway firs, and later on of 

 beeches, the soil becomes enriched with vegetable mould, which 

 binds it together, and enables it to retain atmospheric moisture. 

 The oak then finds an adequate supply of nourishment, and 

 its growth similar to that over the second variety of soil men- 

 tioned while treating of the Permian system. 



2. The Marls accompany nearly all the limes; in the more 

 recent formations, {e.g. Keuper), and play a more important 

 part. On decomposition, they in general furnish a deep, fresh, 

 moderately binding, very fertile clayey, limy, or loamy soil, 

 admirably suited for the rearing of oak forests. But what tree 

 would refuse to orow on such a fruitful soil ? It is chieflv 

 reserved for agriculture, and the forests are mostly confined to 

 hillsides too steep for the plough. It occurs abundantly around 

 Eisenach in Saxe- Weimar, but rarely as forest land, and then 

 producing beech timber with oaks interspersed. 



3. Under the i&vn\ i^ottcrs clays we include the clayey, Intumin- 

 oas, slatey marls, {e.g., of the lower Keuper formation), which 

 form a fertile clay, apt, however, to become wet. It is much too 

 binding for the oak, and is mostly used for agriculture. 



The interspcrsion of the Oak in Beech Forests. — ]\Iixed forests 

 ought to consist of trees which — (1) Thrive well on the same soil 

 and situation; (2) Show no essential difference in their rates of 

 growth ; (3) Fall to the axe at the same time, or in a multiple of 

 that time; (-i) Have different root systems, so that one tree may 

 draw nourishment from the upper layer of soil, and the other 

 from the lower. 



The advantages gained by such mixed forests are — (1) The 

 production of a greater quantity of timber, occasioned by the 

 difference in the root systems, and by tlie fact that the different 

 trees do not seek the same nourishment in equal quantities; (2) 

 Such forests suffer less from the attacks of insects; (3) The resist- 

 ance offered to storms, arising from the difference in the root 

 systems; (4) the timber is applicable to many more uses than if 

 it had been grown in pure forests, and thus a higher revenue is 

 realised. 



The oak is found generally in company with the beech, rarely 

 among silver firs or Norway spruces. On the whole, the oak 

 grows more ra|)idly than the beech, except (a) in exposed situa- 

 tions, and (/S) on shallow soils. However, it is necessary to 

 protect the former against the latter. 



1. By mixing young oaks of 6 to 8 ft. in height with young 

 beeches of 4 to 5 ft. As the former has to remain twice as long 

 as the latter, the oaks should be reared in small circular groups ; 

 for experience has shown that at the time of the natural repro- 

 duction of the beecli such groups do least damage to the young 



