12 GARDEN MANAGEMENT. 



But both chemist and cultivator still confine themselves to generalities. We 

 want to know something more of the origin of soils than we have yet ascer- 

 tained ; for this we must consult the geologist. 



22. From him we learn a strange and wonderful chapter in the history of 

 creation. The framework of the globe we inhabit, he tells us, is a dense mass 

 of primitive rock, of igneous origin, which has been proved by fire and tem- 

 pered by water — vast masses of rugged granite and porphyry towering to the 

 skies in our own and other countries ; overlying which are the rocks of second- 

 ary formation, in which it is sometimes embedded ; but more frequently the 

 shaly slate and old red sandstone ai-e thrown around it in their order of 

 stratification, a mantle, as it were, thrown over the shoulders of these giants of 

 creation. 



23. These rocks of secondary formation are distinguished by their colour, 

 and by their structure, but above all by their fossiliferous remains ; by means 

 of which the naturalist has been able to trace the history of creation through 

 a vast lapse of ages. These rocks of secondary formation, are : — 



24. I. The Silurian group, or clay-slate system, a mass of sedimentary 

 rocks, intersected here and there by beds of igneous origin, in the upper 

 series of which are found the first vestiges of organized beings, 



05. II. The Old Red Sandstone, which can be traced by the naked eye, from 

 the contrast it presents to the grey slate of the Silurian and crystalline masses 

 of the granite rocks, is the next overlying stratum. This difference in colour is 

 the consequence of a change in the beds of ancient seas. During the Silu- 

 rian epoch, the bed of the sea was occupied by a deposit of blackish mud or 

 clay, the debris of granite rock, decomposed by atmospheric influences and 

 thrown down by the action of the waves. In the Devonian epoch, as the 

 system is sometimes called, from its prevalence in that county, this was 

 succeeded by a sandy deposit, mixed with oxide of iron, to which the red 

 colour is due. 



26. III. T/ieCar&o?i?yeroM5 system, embracing the mountain limestone, rises 

 in many places in close connection with the old red sandstone. The latter 

 prevails to a large extent throughout Scotland and Wales ; but if we look to 

 the southern slopes of the mountains, especially in the latter country, they are 

 found to be of another shade ; it is the transition between the Devonian and 

 carboniferous era. The carboniferous rocks develop themselves with great 

 boldness in the vast basins of Glamorganshire, in Caernai-von, and in Carmar- 

 thenshire, and again in Derbyshire, where they occur in bold and picturesque 

 grandevu-, their lofty, pointed, and sometimes fantastic summits melting in the 

 clouds ; the picturesque character of this formation, however, being most ob- 

 servable in the dales or gorges of the mountains. The limestone, which forms 

 the base of the coal-measures, is exclusively of marine origin, as is made evi- 

 dent by the multitude of marine fossils found there : it also contains the first 

 traces of the terrestrial flora, so abundant in the carboniferous formation, or 

 coal-measures. These vegetable ruins become as common in this as they were 

 rare in the previous formations ; they announce immense accessions of dry 



