LESSONS IN GEOLOGY. 



n 



LESSONS l\ GEOLOGY XXVII. 



POST-TEBTIABY OB BECENT PERIOD-CONCLUSION. 



EVERT accumulation which haa been gathered together by any 

 agency since the timoa of the Glacial period, belongs to the 

 Recent or Post-tertiary age. No agent has laid down its power 

 nd ceased to work ; everything now goes on as in tho tim.-* 

 we have been passing through, times whose years we may count 

 by ages. Solomon was wise, and perhaps said moro truth than 

 he at all suspected when he wrote, " There is nothing now under 

 the sun." So that wo may define the Post- tertiary system if 

 * system it can bo called aa that geological work done since 

 the times of the ice and glaciers of the Pleistocene period. 



The Rivers have made deltas, they have scooped out valleys, 

 and worn down rocks into beds of gravel. For their powora of 

 ikin<,' wo must refer the reader to our early leasons, in 

 vrhirh the work done by the Ganges and Mississippi is specially 

 Frequently the river, in excavating a valley, leaves 

 behind it evidences of its labour in river-terraces. These are 

 linen of gravel running along the valley-Bides at different 

 heights ; but there are 

 always corresponding ter- 

 - on each of the facing 

 hills. These terraces mark 

 an old water-level, at which 

 for some time the water 

 stood. It may have been 

 that the valley was blocked 

 up and the water stood at 

 that height, forming a 

 lake, when suddenly the 

 embankment gave way and 

 the water fell to a lower 

 level. The gravel repre- 

 sents the ancient beach. 

 Or if the upheaving move- 

 ment ceased, the river 

 would run at that level for 

 an unusually long period, 

 and when the land again 

 began to rise the current 

 would bo increased, and 

 the erosion of the valley 

 re-cominence with renewed 

 activity. 



These river-terraces, as 

 we shall see, are made 

 peculiarly interesting by 

 the remains of animals and 

 man which they preserve 

 for us. 



Closely allied to the river work are the Lake or Lacustrine 

 Deposits. These are either now in process of being accumulated, 

 or are deposits of mud and silt, intermixed with vegetable drift, 

 which occupy the area once covered by the lake water ; the 

 lake either having been drained by the upheaval of the land, or 

 the hollow which contained its water having been filled up by 

 the debris carried down by the river which supplied it. These 

 deposits contain many skeletons of land animals, together with 

 fresh-water shells, and not unfrequently evidences of the exist- 

 ence of man. 



Similarly, the present work of the sea is to be sought in 

 deposits now in course of being made. Of these, recent dredg- 

 ing has given us some knowledge, though necessarily we are in 

 all but ignorance of the subject. In many places the coast- 

 lino has been greatly altered by the encroachments of the sea, 

 or by the additions made to it by the deposits left by the water. 

 Tyro and Sidon, the oft-mentioned sea-ports of Scripture, are 

 now several miles inland. We owe to the sea, as a recent gift, 

 the fens of Lincolnshire and Cambridge, the 300 miles of 

 Humber "warp." Other countries are far more indebted; 

 Holland and Denmark are well nigh wholly the product of the 

 German Ocean, deposited in the last of geological periods. 



The Volcanoes, now in action, also add their quota to " recent" 

 productions in the beds of lava, scoriae, and ashes which they 

 have ejected during the " Post- tertiary " period. 



Antiquity of Man. But by far the most interesting subject 

 this period introduces to UB, is the appearance of man on the 

 150 N.E. 



ARROWHEADS : 1. MISCARN, DESERTMAETIN, Co. DERBT. 2. VALLET OF THE 

 SOMME. 3. HFELAHAKS, NEAR TULLTMOHE. 4, 5. IRELAND. 6. PEKC. 

 7. NORTH AMERICA. 



earth. It U evident that we shall be warned of his 

 either by the discovery of human skeletons, at by findinf indi- 

 cation* of hi* presence in some of his works. 



We shall speak of the latter Brat. The works of the Miflsjf 



members of our race, of whom we hare at prsssnt found say 

 record, are always the knives, arrow and spear beads, hatchets, 

 hammers, which are the essential implements of savage Ufa. 

 The material and workmanship of these took mark the suc- 

 cessive stages of civilisation through which cur forefathers 

 passed. The earliest instruments are of stone ; then, as men 

 gained experience and discovered the rudiments of metallurgy, 

 bronze, an alloy of tin and copper, took the place of stone) 

 and as civilisation still further advanced, and the more difficult 

 exploit of reducing iron from its ore was achieved, the bronze 

 gave way to the more useful iron. 



The ages in which these successive stages were in progress 

 are termed the Stone age, the Bronze age, and the Iron age. 



In the stone age there is also a marked progression. The 

 earliest implements wore made of flint, chipped into the 

 required shape by hand. The regularity of the arrow and 



spear heads is often re* 

 markable ; but flint is 

 more readily worked than 

 at first might be supposed, 

 and there are now many 

 men in England who are 

 adepts in chipping flint, 

 and producing stone im- 

 plements which are palmed 

 off upon the credulous 

 public as the handiwork 

 of our savage ancestors. 

 Although it may appear 

 strange, it is said that the 

 flint chips more readily 

 when worked with another 

 flint than if an iron tool 

 be used ; so that we need 

 not be surprised at the 

 clever specimens of stono 

 handicraft preserved for 

 us in the gravels and cave 

 deposits of the Post-ter- 

 tiary period. 



In due time, however, 

 the plan of grinding the 

 flints was resorted to, and 

 the consequence is that 

 the implements at the 

 hitter period of the stone 

 age exhibit more skilled 



workmanship. This improvement in the stone implements has 

 divided the age into Neolit'iic and Palaeolithic ages. 



The Palaeolithic age is the older portion of the stone period, 

 and is marked by the hand-chipped flints. The ancient people 

 who fabricated these implements lived in Northern France and 

 in the south of our island. In the river gravels of Abbeville 

 and Amiens, in 1847, M. Boucher de Perthes found many sped, 

 mens of their handicraft. These beds of gravel vary in their 

 height above the present bottom of the valley from 20 to 200 

 feet. This depth indicates the amount of coooping work the 

 river has done since these ancient occupiers of the country 

 pitched their wigwams on itd banks. These tools are usually 

 bleached by long exposure to the air, or they are stained with 

 the same yellow tinge which pervade* the gravel-bank, and 

 sometimes crystalline incrustations of carbonate of lime appear 

 upon their surface. Their edges are blunted either by wear or 

 by the rolling action of the water, and they are usually found 

 at depths of fifteen to twenty-five feet from the surface. 



The fact that the Somme has excavated as much as 200 feet 

 of valley since the people of the early stone age hunted upon 

 its banks, may impress us with some notion of the lapse of 

 time since that very remote period, yet the positions in which 

 similar rude flint instruments are found in England carry our 

 minds yet more forcibly back into the long past. On the tops 

 of the hills in South Hampshire, and in the north of the Isle of 

 Wight, masses of gravel are found. These detached beds are 

 evidently but remnants of a great deposit of drift resting on the 



