AGRICULTURAL CHARACTERS OF THE OLD RED SYSTEM. 



193 



Colva Hill. In the farms of Llanhowel and Foyce, the strata rising into a low hill are 

 vertical, and consist of greenish, red, and chocolate-coloured, thin-bedded, micaceous 

 sandstones, flanked on the east, near Gladestry, by traces of impure cornstone and 

 mottled concretionary marl. The direction of the ridge is from north-north-east to 

 south-south-west, and the Silurian rocks which flank it, are parallel and also highly 

 inclined. 



We shall recur to the form, direction, and highly elevated position of these stripes 

 of Old Red Sandstone to the south of Presteign in a subsequent chapter, after the 

 intrusive rocks which have affected this district have been described. It is sufficient 

 to state in this place, that beyond all doubt, these outliers have been separated from 

 the chief mass of the system by elevatory forces, which erupting the igneous rocks, 

 upheaved the inferior strata, and caused great denudation in the overlying deposits. 



Wherever these outliers occur, the agricultural surface presents a marked contrast to 

 that of the surrounding grey tracts of the Silurian System, being in fact repetitions on 

 a small scale of the large basin occupied by the Old Red System. 



Agricultural Characters of the Old Red Sandstone. 



The decomposition of strata so different in character as those which constitute this 

 system, naturally gives rise to soils of dissimilar qualities. In those high and moun- 

 tainous tracts which are principally occupied by the upper formation of quartzose con- 

 glomerate and sandstones, the soil is light, sharp, and little productive. In the corn- 

 stone group, on the contrary, the disintegration of calcareous nodules, and the admixture 

 of their component parts with the argillaceous and sandy particles of the other strata, 

 produce the well-known, rich, red soil of Herefordshire, in the greater part of which an 

 argillaceous character prevails. The most loamy of these marls afford the finest crops 

 of wheat and hops, and bear the most prolific apple and pear trees ; whilst the whole 

 region (eminently in the heavier clayey tracts) is renowned for the production of the 

 sturdiest oaks, which so abound as to be styled the " weeds of Herefordshire." Thus, 

 although this region contains no mines, the composition of its rocks is directly pro- 

 ductive of its great agricultural wealth. 



As some of the characters here described, are also common to the lands of the New 

 Red Sandstone, so in that case, are the results due, to the decomposition of rocks 

 similar in structure to those of the Old Red ; for it has been previously indicated, 

 that the spotted marls and concretionary limestones of the two systems are often un~ 

 distinguishable. (See Chapters 3 and 4.) 



The concretionary limestones are so abundant, that there is scarcely any part of the 

 central districts of Herefordshire where lime-kilns are not numerous. But this lime, 

 being itself much impregnated with argillaceous matter, is not always well adapted to 

 the soil, particularly where the clays prevail; and hence whenever the inhabitants lie 



