♦ KNOWLEDGE ♦ 



[July G, 1883. 



GEOLOGY AND AGRICULTURE. 



By J. Vincent Elsden, B.Sc. (Lond.), F.C.S. 



IN a couutry like England, in which a day's journey is 

 sufficient to traverse rocks of every geological age, 

 even the most careless observer cannot tai^ tc lie struck by 

 the diversity of appearance presented by the difterent 

 strata over -which he travels. The stifl" soils of the eastern 

 boulder-clays, the sheep-farming of the chalk downs, the 

 pasture-land on the cold clays of the Midland Courties, the 

 rich land on the Old Red Sandstone, and the ban r. aspect 

 of the rugged Silurian rocks of Wales all point to the fact 

 that each of the great geological systems is characterised by 

 peculiar agi-icultural features. But, in England, much of 

 the contrast Ijetween the various formations is lost owing 

 to the great extent to which the underlying rocks are 

 covered up by superficial accumulations, which entirely 

 change the character of the soO. 



In Belgium similar differences are to be observed between 

 the desolate plateau formed by the Palfeozoic rocks of the 

 Condroz and Ardennes, the fertile Hesbayan loam of the 

 central parts, the barren Campine sands, producing only 

 heather and pines, and the rich alluvial soil of the 

 Polders. 



In Norway, the fjelds, or elevated plateaux, which 

 occupy more than half its area, are perfectly barren ; and, 

 ill Sweden, the cultivated tracts coincide with the deposits 

 •of glacial clay and marl, which cover up the gneiss and 

 granite. 



From the alluvial deposits forming the two immense 

 plains of Hungary, one of the richest soils of Europe has 

 been formed, and the chief source of the agricultural wealth 

 of Russia is the recent deposit, known as the Tchornoi-zem, 

 or black earth, which occupies the valleys of the Don, 

 Dnieper, and Volga. 



In America, the connection between geology and agri- 

 culture is still more marked. The sudden transition from 

 the fertile alluvium of Virginia to the barren sands, clothed 

 with pine forests, which characterise the Tertiary beds ; 

 the dry chalk downs and treeless prairies, famous for 

 Georgian wheat, which mark the Secondary deposits, and 

 tlie general hu.sbandry and fertile soils of the Primary 

 rocks, forming the lower parts of the Alleghanies, show the 

 geological features of the country almost as perfectly as 

 would a careful survey of the underlying rocks. 



It is not to be supposed, however, that these differences 

 ill agricultural features are due to the character of the soil 

 alone, for climate has as much influence as soil in modi- 

 fying agricultural operations ; but since climate is regu- 

 lated mainly by contour, and contour depends chiefly upon 

 geological structure, there is the same primary cause for 

 variations in both cases. Nor must it be forgotten that it 

 i.5 the tendency of improved systems of agriculture to over- 

 come all obstacles to the growth of crops, even in soils 

 which are naturally unsuited to them ; and thus the 

 natural diversity of character which formerly existed is, 

 to a great extent, destroyed. This is especially noticeable 

 in the impro\ement of large tracts formerly regarded as 

 V astes, and in the breaking-up of permanent pasture. For 

 ii'.stance, the agricultural features of the chalk districts of 

 England are by no means so marked, now that they have 

 V..:-en invaded by the plough, as they were when in rolling 

 downs and sheep pastures only. But in these cases the 

 improvement is artificial, and the natural conditions would 

 reappear if constant attention were not paid to the mainte- 

 nance of the soil in an improved state. To the ordinary 

 oViserver the appearance of a naturally fertile soil, and of a 

 barren soil, rendered artificially jjroductive, may be very 



much the same ; but to the farmer the difference is ex- 

 treme, for while the former is worked with ease, the latter 

 can only be made to yield good results by endless trouble 

 and expense. 



Hence it is seen that not only do the natural agricultural 

 capabilities of the soil vary with the geological structure of 

 the rocks from which it is derived ; but also that facilities 

 for improvement and the amount of attention necessary to 

 pre\ent deterioration are similarly influenced. 



The natural vegetation of any locality is so entirely de- 

 pendent upon the nature of the soil, that the geologist often 

 receives great assistance, in mapping the boundary-lines 

 between different strata, from careful observations of the 

 plants which grow there. For instance, it is most inte- 

 resting to note how that beautiful heath, Erica Vagans, 

 which grows upon the serpentine of the Lizard district, in 

 Cornwall, marks out the boundary of the barren serpentine 

 from the fertile soils of the adjoining rocks. Buckland, 

 writing in 1S40, describes a moor in Dumfries, in which a 

 band of bright green herbage marked the course of a trap 

 dyke traversing slate rocks. Similarly, in Staffordshire 

 the line of junction of carboniferous limestone and mill- 

 stone grit is very clearly drawn on the surface by the 

 sudden change in the quality of the grass, and four plants 

 in particular mark the exact spot where soil changes — the 

 furze, the heath, the whortleberry and the sorrel. In 

 Hertfordshire, the Ijoundary-line of the London clay is 

 frequently defined by a verge of grass-land, which termi- 

 nates with the out-crop of the chalk ; while in the New 

 Forest, the presence of the taller furze is a certain indi- 

 cation to the farmer that the land below is worth reclaiming. 

 In many cases, also, particular formations are characterised 

 by the trees which grow upon them. In Surrey, the Gault 

 is distinguished by the luxuriant growth of oak and elm ; 

 while the Weald clay has long been noted for the perfection 

 of its oaks. Beech trees abound on the chalk formation, 

 and elms flourish on London clay, while the famous oaks of 

 Bugot's Park, in Staflbrdshire, mark the position of an out- 

 lying patch of Lias. It is well-known that the districts 

 most celebrated for their cider are situated on the corn- 

 stones and marls of the Old and New Red Sandstone 

 formations, and, in Scotland, the Carse of Gowrie, so 

 famous for its apples, stretches over the Old Red 

 strata. 



To such an extent, indeed, is vegetation influenced by 

 soil and climate, that the experienced farmer can form an 

 opinion as to the fertility of the land from the species of 

 plant growing upon it. For this reason many parts of the 

 British Isles have remained to this day untUled, forming 

 the moorlands and heath-covered wastes so characteristic of 

 many geological strata. But even a naturally fertile soil 

 is frequently rendered unproductive by deficient water- 

 supply or defective drainage. The scarcity of water in 

 chalk districts is a source of continual trouble and expense 

 to the farmer, who is obliged to sink deep wells, at a very 

 great cost, or to depend upon the supply afforded by arti- 

 ficially constructed dew-ponds. In Alabama, the dryness of 

 the chalk soils is a great hindrance to agriculture, for only 

 farmers of large means can afford to undertake the deep 

 boring necessary to obtain a supply of water. A similar 

 scarcity of water is experienced on account of the extreme 

 porosity of the Oolitic soils of the Cotteswolds. On the 

 other hand, a farmer who is located upon imperious clays 

 is put to no less an expense in getting rid of superfluous 

 water by draining his land. Even upon porous rocks like 

 the Old Red Sandstone, liogs are frequent on account of 

 the sand becoming cemented into a hard mass, by means of 

 oxide of iron, thus forming an impermeable pan. 

 (To be continued.') 



