HARDWICKE'S SCIENCE-GOSSIP. 



an insignificant part of a great and continuous rocky 

 stratum. What this rock was composed of, matters 

 little or nothing-, for we "Glacial Boulders" have no 

 such clannish feeling as other geological story-tellers. 

 We are composed of all kinds— and the bed of clay 

 in which we have been deposited may be regarded 

 as a sort of lithological Parliament, in which the 

 representatives of every formation are assembled. 

 But allow me, if you please, rapidly to sketch the 

 outlines of the events which transpired before I was 

 ruthlessly wrenched from my original rocky home, 

 and transposed into a boulder. 



As many of my hearers are aware, the earlier part 

 of the Tertiary period was, in England and else- 

 where, marked by an almost tropical climate. During 

 the Eocene epoch, the seas of our latitude were in- 

 habited by 'shells and fish of tropical types. The 

 dry land was clothed with tree-ferns, palms, &c, 

 and these gorgeous forests were frequented by huge 

 serpents, strange-looking, tapir-like quadrupeds, aud 

 monkeys. The rivers, also, had their alligators and 

 crocodiles. In short, all the types of land, fresh- 

 water, and marine fauna and flora, which now distin- 

 guish equatorial regions, existed in England. The 

 rocks of this period are full of proofs of the truth of 

 what I say. Then gradually succeeded the Miocene 

 epoch, during which the climature was less torrid- 

 Even then, the great arctic ice-cap had not been 

 formed at the pole, for we have abundant evidence 

 that countries situated far north, such as Greenland 

 and Spitzbergen, were covered with vegetable forms 

 nearly allied to those now living in South Carolina, 

 Japan, the Cape of Good Hope, and Australia. 

 Then succeeded the Pliocene age, whose climate is 

 abundantly indicated by its fine " Crags," as the 

 beds of shells are termed. The oldest of these is 

 called the " Coralline," and there may be found in 

 it no fewer than twenty-seven species of shells, 

 nearly allied to or identical with those now existing 

 in southern latitudes. The "Red Crag" comes 

 next in ago, and this tells you by similar evidence 

 that the climate was gradually getting colder, for 

 the number of southern shells has dwindled to thir- 

 teen, whilst there has appeared in English latitudes 

 species allied to those now living iu northern seas. 

 Einally, the third, or "Norwich Crag," supplements 

 the teachings of its relatives by its total absence of 

 southern shells, and its much greater proportion of 

 arctic species. Another bed of Crag, situated some 

 height above this, still further corroborates the 

 remarkable fact I have been narrating, for its 

 greater abundance of northern forms is as remark- 

 able as that of the older Norwich Crag over the rcd- 

 About the same age as the latter bed is a pheno- 

 menon, known as the " Forest bed," which crops out 

 from beneath the steep cliffs along the Norfolk and 

 Suffolk coasts. It is the site of an old forest, now 

 paving the bottom of the German Ocean, and the 

 imbedded stools of trees, as well as those of land and 



freshwater plants, indicate a temperate}[mildness of 

 climate, similar to that now marking the British 

 islands — or, if anything, a trifle colder, as the pre- 

 sence of the Scotch fir and Norway spruce pine clearly 

 shows. 



My hearers cannot but be struck with the gradual 

 refrigeration of climate, from tropical or subtropical 

 conditions, to a temperate one. Meantime, the slow 

 but sure change from a warmer to a colder physical 

 circumstance clearly prophesied that the next period 

 would probably be marked by the same law. Such 

 proved to be the case. The change of climate indi- 

 cated by the several periods I have mentioned, 

 culminated in that "Glacial period" during which 

 my birth as a boulder took place. 



After the epoch of the " Crags," a gradual subsi- 

 dence of England, as far south as what is now the 

 Thames slowly took place. Little by little the 

 whole country sunk beneath the sea, in which, 

 with increasing depth, there came increased arctic 

 cold. The greater part of Scotland — certainly 

 the whole of the Highlands— were covered with 

 glaciers, or sheets of accumulated snow, frozen into 

 ice. The snow-line — which in England is now some 

 thousands of feet above the ocean-level — then was 

 gradually lowered by the greater cold until it was 

 met with as low as it could possibly creep. The 

 hills of North Wales, Cumberland, Lancashire, and 

 other places also had their ice-cap. To what thick- 

 ness this great ice- sheet accumulated, or what course, 

 I can form no idea; but if it was anything like what 

 now takes place in Greenland— and I have every 

 reason for asserting that England at the time of 

 which I am speaking, experienced Greenlandic cir- 

 cumstances, rather than those of any other part of 

 the world — then this sheet of snow or ice possibly 

 grew to be hundreds, if not thousands, of feet in 

 thickness. Such is the case in Greenland at the 

 present time. The fine snow accumulates on the 

 mountain-tops, and is only got rid of by its freezing 

 into a sheet, which is always moving down to the 

 lowest level. In temperate and tropical climates, 

 rivers carry off the excess of moisture — in arctic 

 countries this can only be done by the moving ice- 

 sheets, termed " glaciers." The Greenland glaciers 

 debouch into the sea itself. The ice-sheet forms 

 grand sea-cliffs, hundreds of feet high, along whose 

 bases the angry sea eats caverns, until the toppling 

 mass falls over, and iloats away as an iceberg. Or 

 the great ice-sheet thrusts itself right into the sea,, 

 creeping along its bottom until it comes to water 

 deep enough to buoy up, break off, and float away 

 the extreme end. 



You will have no difficulty in perceiving that 

 the immense mechanical force exercised by such 

 glaciers on the solid hard rocks over which they 

 creep must be immense. You can easily conceive 

 how the latter must be ground down and pounded 

 into mud ; and also, how fragments would be broken 



