OCR Text |
Show 70 ERA OF THE SUPERFICIAL ItOR.MATIONS. tiaries in England is disturbed by t~o great s~ells, fo!m"' incr what are called anticlinal axes, one of wh1ch diVIdes th~ London from the Hamp~hire basin, while the other passes through the Isle of vVight, both throwing the.strata down at a violent inclination towards the north, as If the subterranean disturbing force had waved forward in that direction. The Pyrenees, too, an~ .Alps, have bo!h ~ndergone elevation since the deposition of the terbanes; and in Sicily there are mountains which have risen three thousand feet since the deposition of some of the n1ost. re· cent of these rocks. The general effect ofthese operations was of course to extend the land surface. and to increase the variety of its features, thus improving the natural drainage, and generally adapting the earth for the reception of the higher classes of animals. • ERA OF THE SUPERFICIAL FOR1\1ATIONS COMMENCEMENT OF PRESENT SPECIES. WE have now completed our survey of the series ot stratified rocks, and traced in their fossils t1e progress of organic creation down to a tjm~ which seems not long antecedent to the appearance of man. There are, nevertheless, monuments of still another era or space of time, which it is all but certain did also precede that event. Over the rock formations of all eras, in various parts ot the globe, but confined in general to situations not very elevated, there is a layer of stiff clay, mostly of a blue co· lor, mingled with fragments of rock of all sizes travel· worn, and otherwise, and to which geologists give the name of diluvium, as being apparently the produce of some vast flood, or of the sea thrown into an unusual agitation. It seems to indicate that, at the time when it \Yas laid down, much of the present dry land was under the ocean, a supposition which we shall see supported bv other evidence. The included masses of rock have bee;1 carefully inspected in many plac-es, and traced to particular parent beds at considerable di~tances. Connected with these phenomena are certain rock surfaces on the slopes of hills and elsewhere, which exhibit groov.ing3 and scratchings, such as we might suppose would be pru COM.M.:ENCEMENT OF PRESENT SPECIES. 71 duc.ed by a quantity of loose bl?cks hurried along over them by a fio·od. Another associated phen'(nnenon is that called <:nLg a~d !ail, which exists in many places namely a_ rocky rnountain, o.r lesser elevation, presentin'(J' on on; side the naked rock in a more or. less abr~pt f~rm, and QD the other ~ gentle slope; the sites of Windsor Edinb~ rgh, and Stu·ling; with their respective castles, ~re speCI! llens of .crag and taiL FinaUy, we may advert to cer t~In long ndges of clay and gravel which arrest the attention of ~avellers on the sllrface of Sweden and Finland !lnd which are also found in the United States, where; Indeed, the whoie of these phenomena have been observed ov~r a large surface, .as ~ell as in Europe. It is very rema1kable that the direction from which the diluvial blocks have ~~nera.Hy come, the lines of the grooved rock surfaces, the cllrechon of the crao- and tail eminences and that of the c1a:y and gt·avel ridg~s-phenomena, he it observed, ex.tendi ng over the northern parts of both Europe and Amenca-a,·e all from the north and north-west towards the sottth-east. We thus acquire the idea of a powerful current ~oving ~n a direction from north-west to south-east, car.rying, bes1des mud, masses of rock which furrowed the so ltd surfaces as t~ey passed along, abrading ~he nol'th-w~st f~ces ?f ma~y .hills, but leaving the slopes In th~ oppos1t<=: dll'ectwn uninJured, and in some instances forming long nd.ges o~ detritus along the surface. These are curw~s considerations, and it has become a question of much Interest, by what means, and under what circumstances, was such a cu~r~~t produc?d· One hypothetical a_nswer l1as some plaust~Ihty about It. From an investigation of ti:e n~t ure of glaciers, and some observations which seem to Indicate tha~ thcs~ have .at one time extended to lmver levels, and extsted In regions (th.e Scottish Highlands an example) w·hcre there is no perennial sno·w it has bee~1 surmised that ther~ was a time, subsequent' to !he tertiary era, when the Circumpolar ice extended far Into th.e temperate ~one, and formed a lofty, as well as ex~ensi:e ac?umulatwn. A change to. a higher temperatute, productng a sudden thaw of this mass mio-ht set free such a quantity of water as would form a iarg~ flood and .the s_o~tlnyard flow of this deluge, joined to the di~ rect10n wr11ch 1t would obtain from the rotary motion of the globe, woulc~ of ~ourse . produce that compound or south-ea~tt"!rl y duechon whiCh the phenomena require |