22 



THE FARMER'S MAGAZINE. 



chalk range of the North Downs, partially covered 

 on the north by the clays and sands which form the 

 lowest group of the tertiary series, as the strata 

 above the chalk are called. The narrow valley of 

 Helmsdale, which skirts the base of the chalk 

 escarpment, is composed of the gault, a dark, tena- 

 cious clay, which crops out or emerges from beneath 

 the chalk, the strata not being horizontal, but in- 

 clined at a small angle. 



The broken range of hills which lies to the south 

 of the valley, and forms the picturesque country 

 about Seven Oaks, is the lower greensaud. The 

 upper greensand, in this part of its rauge, is merged 

 in the chalk, or forms a very thin baud at its base, 

 concealed under the debris of the chalk escarpment. 

 Further to the west, in the neighbourhood of Farn- 

 ham, it expands into strata of considerable thick- 

 ness. The sandy beds of the lower greensaud have 

 been worn away by the denuding action of marine 

 currents to which they were exposed when the laud 

 was emerging from beneath the sea, while their 

 liarder portions have resisted that action and form 

 the hills. South of this range lies another clayey 

 tract, the basis of which is the Weald clay. From 

 beneath that clay, agam, rises the central ridge of 

 the Hastings sands, so called from the sea cliffs 

 which they form near Hastings. From this central 

 ridge the strata dip away both to the north and 

 south, so that we Lave a repetition of the same strata, 

 forming similar areas on each side of it, the gault 

 aud the lower greensand sinking in opposite direc- 

 tions under the chalk which forms the ranges of the 

 North and South Downs. 



One remarkable feature of the Wealden area is 

 that all its rivers, instead of flowing in the same 

 direction as the Thames, escape to the north and 

 south through gorges in the chalk. Those which 

 rise south of the central ridges of the Hastings 

 sands empty themselves into the sea on- the south- 

 ern coast, while those which flow northwards from 

 it— as the Darent, the Mole, aud the Wey — pour 

 their tributary streams into the Thames. 



The succession of beds which have been described 

 as emerging from beneath one another in the centre 

 of Kent form, however, only a small portion of the 

 stratified series. Below them arc many great groups 

 of strata, consisting of numerous alternations of 

 sand, clays, and limestones, having a collective thick- 

 ness of several miles. For the purposes of classifi- 

 cation, these have been divided into four great natu- 

 ral groups, which are distinguished from each other 

 by peculiarities in then* fossil contents. These four 

 principal groups arc again divided into minor groups 

 — systems, as they are called — distinguished in like 

 manner from one another by minor differeuces in 

 their fossils. All these beds have becu, during loug 

 periods, successive sea-bottoms; aud the fossils 

 which they contain are the remains of plants and 

 animals -which lived ou the land or in the waters 

 while the strata were being deposited from the -waste 

 of pre-existing land. # 



By forces acting from below, these successive sea- 

 beds have been raised out of the water aud converted 

 into dry land. We have also evidence not to he 

 mistaken, afforded by the fossil contents, that the 

 same areas have been repeatedly elevated above the 

 sea- level, and again depressed below it, 



From below the stratified rocks thus spread out 

 in broad sheets, other rocks have been protruded ; 

 sometimes in a solid, sometimes in a molten state, 

 similar to those which are new forming froni the 

 melted lava poured out from volcanic craters, either 

 on the laud or beneath the sea. These outbursts of 

 melted matter, which constitute the irregular masses 

 of the unstratified rocks, have at differeur periods in 

 the earth's history thrown the once horizontal sea- 

 bottoms into highly-iuclined positions, and have 

 formed the different mountain-chains by -which the 

 surface of the earth is so beautifully diversified. 



By means of these fractures aud dislocations, and 

 by means of the sections exhibited in sea-cliffs, we 

 obtain a knowledge of the structure of the earth to 

 depths beyond those of the deepest mines. From 

 those parts of the stratified series which have been 

 disturbed in each chain of hills, and those parts of it 

 which repose upon them horizontally or abut against 

 them, we obtain a knowledge of the curious fact 

 that different chains of mountains aud ranges of hills 

 have been thrown up at different periods. The 

 fracture of the chalk which exposed the strata below 

 it, forming the surface of the Weald, was one of the 

 most recent of these disturbances. 



The four great groups into which the stratified 

 series is divided, begimiiug with the lowest, are, 1, 

 the azoic, or strata destitute of organic remains ; 2, 

 the palaBOzoic, or group of ancient life ; 3, the mezo- 

 zoic, or group of middle life ; 4i, the kainozoic, ov 

 group of modern life, more generally known by its 

 long-established but less appropriate name of the 

 tertiary series. 



We are sorry to be obliged to use hard names, but 

 there is no help for it. Compounds from the Greek 

 and Latin express, in one word, a brief description 

 of the thing referred to, which in our language can 

 only be expressed by several, and are therefore the 

 best when new names are required. Scientific names, 

 moreover, are designed for use in all parts of the 

 world, and require to be such as can be understood 

 by the educated classes of all nations. 



As the azoic or uou-fossiliferous strata have, in 

 many cases, undergone considerable alteration from 

 contact with heated subterranean masses, some con- 

 tend that they once contained fossils, which have 

 been obliterated by the heating process ; but as there 

 are, in many places, a considerable thickness of 

 strata of this kind which have not undergone any 

 heating process, and- are equally destitute of organic 

 remains, that opinion cannot be maintained. 



With respect to the different classes of animal 

 life which distinguish these four great groups, the 

 palaeozoic era was the epoch of fishes. They were 

 the most highly organized class of vertebrate auimals 

 called into existence during the period of which 

 those rocks record the history. The mezozoic, or 

 group of middle life, was the era of a more highly 

 organized class of vertebrates. The dynasty of the 

 ■ reptiles, and the tertiary or kainozoic, was the era 

 of warm-blooded animals, the mammals or sucklers. 

 It was not till the close of these four great periods 

 that man became a denizen of earth. 



The four principal groups above-mentioned con- 

 tain many minor groups, distinguished in like man- 

 ner by minor peculiarities in the fossil contents. 

 The azoic group, for instance, is composed of a sue- 



