3i 



THE FARMER'S MAGAZINE. 



rocks. The majority of English geologists, however, 

 regard the Neacomian fossils as those of the lower 

 greensand, aud as having a greater affinity with the 

 cretaceous than the oolitic group. 



Let us now examine the details of the tertiary or 

 kainozoic series — the series more recent than the 

 chalk. Up to the termination of the cretaceous 

 epoch, all the species, and most of the genera, are 

 extinct. lu the tertiary series existing species begin 

 to make their appearance, and continue to increase 

 through a thick succession of deposits, which indi- 

 cate a long lapse of time ; until at length, in more 

 recent deposits, we meet with that group which is 

 cotemporaneous with man. This change was 

 gradual. Old races became extinct, and new ones 

 were introduced to supply their places. 



From these facts, the tertiary series has been 

 divided into four groups, according to the propor- 

 tion of shells belonging to the existing species which 

 they contain. 



Having been deposited in seas of more limited 

 extent than those in which the strata of the earlier 

 epochs were formed, the order of superposition — 

 that infallible test of age — is not always available ; 

 nevertheless it is sufficient to confirm the correct- 

 ness of the classification founded on the iacreasing 

 proportion of existing species. Arranged and named 

 on this principle, the divisions of the tertiary series, 

 commencing with the lowest, are the eocene, 

 miocene, pleiocene, and pleistocene. We again 

 apologise for the Greek words from which these 

 names are derived. They signify that, in the eocene, 

 in which there are only ten per cent, of the species 

 now living, we see the dawn or commencement of 

 existing races ; that in the miocene, in which they 

 amount to iwenty per cent., they are still in the 

 minority ; while in the pleiocene, or more recent, they 

 cousiitute the majority, for only about ten per cent, 

 are extmct. In the pleistocene, or most recent, the 

 proportion of extinct species does not exceed five 

 per cent. 



The eocene, or older, tertiaries of England occur 

 in two separate areas, known as the London and 

 Hampshire districts. From the intervening de- 

 tached portions, in geological language "outliers," 

 which occur in the intervening space up to the very 

 edge of the chalk escarpment, it is evident that 

 these two districts were once united. We have 

 thus evidence that the fracture aud denudation of 

 the chalk, and the exposure of the inferior strata in 

 the Weald, took place during some portion of the 

 tertiary era. We shall show hereafter that it was 

 towards the close of it. 



The lower eocenes comprise the following division 

 iu the ascending order : — L The Thanet sands ; 

 2. The Reading beds, called also the plastic or 

 mottled clay ; 3. The Woolwich beds, or basement 

 beds of the London clay; 4. The London clay, or 

 Bagshot beds. The middle eocenes comprise : — 

 1. The lower Bagshot or Bournemouth sands and 

 clays; 2. The middle Bagshots or the Brackle- 

 sham sands and Barton clays ; 3. The upper Bag- 

 shots or the Headon-hill sands. 



The first in each pair of names in the preceding 

 list i£ that by which they are known in the London 

 district : the second is that of their Hampshire 

 equivalents. 



This classification and nomenclature of the eocene 

 strata of England has only lately been established, 

 and are not to be found iu any published geological 

 maps or elementary treatises. It will be seen that 

 Kent is the typical region where many of these de- 

 posits may be best studied. 



In Alum Bay, and in Whitecliff Bay, in the Isle 

 of Weight, the whole of the eocene series is exhibited 

 within a short space, having been thrown into a 

 vertical position, which gradually resumes its 

 original horizontal state in the northern side of the 

 island, and in Hampshire. All the eocene strata are 

 applied to a variety of important economic uses. 

 There is the glass-house sand of Alum Bay, so 

 named because from some of its clays alum was 

 formerly made. The London plastic clays, in the 

 London and Hampshire districts, are largely em- 

 ployed iu the manufacture of bricks aud tiles. 

 Beautiful wbite bricks, equal to those of Suffolk, 

 which are also derived from clays of the eocene ter- 

 tiaries, are manufactured from the calcareous clays 

 of the upper eocenes. 



The beds of the pipeclay of the lower Bagshots 

 are largely exported from Poole to the pottery dis- 

 districts, and the refuse clay from the same pits — 

 too much contaminated witii metallic salts to burn 

 ot a pure while colour — is now much in demand for 

 making the stoneware employed for bottles, and for 

 the vessels capable of resisting the action of acids 

 required by the manufacturing chemists. This in- 

 ferior clay is also in great demand for the manufac- 

 ture of draining-pipes so extensively used of late for 

 the smaller sewers of towns. 



Let us now take a rapid glance at the changes in 

 organic life indicated by the period from its commence- 

 ment iu the lower part of the palceozoic division to 

 the close of the older terliaries. It has been already 

 stated that during the ))alfeozoic epoch fishes were 

 the dominant race. 



The earliest known fishes make their appearance 

 in the base of the upper Silurian rocks. Between 

 this period and that of the lingula bed, at the base 

 of the lower Silurians, there had been a large deve- 

 lopement of invertebrate life — of molluscs, to which 

 the oyster, the whelk, and the limpet belong — of 

 zoophytes (corals, aud other animals allied to them)^ 

 crustaceous, or animals of the class to which the 

 lobster, the crab, and the shrimp belong. The seas 

 had swarmed with them in still increasing numbers, 

 both of species and individuals, through the whole 

 series of deposits, the most highly and the least 

 organized of each dass making their appearance 

 simultaneously, and thus refuting the dogma so in- 

 dustriously circulated of late, that one was derived 

 by descent from the other. Fishes at length make 

 their appearance at the point of time which we have 

 elsewhere designated. They became very abundant 

 during the formation of the old red sandstone. In 

 the coal measures some of the large predaceous 

 fishes were of a higher organization than most of 

 the existing races — approaching the reptile class in 

 some points of structure. 



The old red sandstone, once deemed destitute of 

 fossils, has yielded to the researches of Agasses, the 

 gi'eat authority in the natural history of fishes, 

 nearly as many species as are known in our present 

 seas. They differ widely, however, iu structure 



