August 1, 1900.] 



KNOWLEDGE. 



171 



Origin of the Earthquake. 



The above facts all point to a complex origin of tho 

 eaa-thqiiake. There may have been a number of com- 

 pletelv separated foci, giving rise to a group of nearly 

 concuiTcnt shocks. Or, and this is a far more probable 

 supposition, there may have been one great deep-seated 

 focus, from which off-shoots ran up towards the surface. 



As Mr. Oldham points out, we have recently become 

 acquainted with a structure exactly corresponding to 

 that which is here inferred. The great thrust-planes, 

 so typically developed in the Scottish Highlands, arc 

 onlv reversed faults which arc nearly horizontal in- 

 stead of being highly inclined ; but they are accom- 

 panied by a number of ordinary reversed faults running 

 upwards to the surface. In Fig. 2, the main features 



T T T T 



Fio. 2. — Diagram of Thrust-pUnes and llinor Thrusts. 



of a section drawn by the Geological Survey of Scotland 

 are reproduced ; TT representing thrust-planes, and tt 

 minor thrusts or faults. A great movement along one 

 of the main thrustrplanes could not occur without corre- 

 sponding slips along many of the secondary planes. No 

 direct effect of the former might be visible at the 

 surface except in the horizontal displacements that 

 would be rendered manifest by a trigonometrical survey ; 

 whereas the latter might or might not reach the surface, 

 giving rise in the one case to fissures and faults, and 

 in the other to local changes of level. 



This, it should be remarked, is only a probable ex- 

 planation. Others might be offered that would account 

 equally well for some of the phenomena, but none, Mr. 

 Oldham thinks, so completely for all the facts observed. 



If the main part of the focus were continuous, as this 

 theory would imply, its enormous dimensions will be 

 evident from the facts that have been described. Mr. 

 Oldham has traced the probable form of the epicentre. 

 It may not be quite so simple or symmetrical as is 

 represented by the continuous line in Fig. 1, but there 

 are good reasons for thinking that it does not differ 

 sensibly either in size or form from that laid down. 

 The part of the thrust-plane over which movement took 

 place must therefore have been about 200 miles long, 

 not less than 50 miles wide, and between 6000 and 

 7000 square miles in area. With regard to its depth, 

 we have no decisive knowledge. It may have been 

 about five miles or less ; it can hardly have been much 

 greater. 



It is a strain on the imagination to try to picture the 

 displacement of so huge a mass. We may think, if 

 we please, of a layer of rock, three or four miles in 

 thickness and large enough to reach from Dover to 

 Exeter in one direction, and from London to Brighton 

 in the other, not slipping intermittently in different 

 places, but giving way almost instantaneously through- 

 out its whole extent; crushing all before it, both solid 

 rock and earthy ground indifferently; and, whether 

 by the sudden spring of the entire mass or by the jar 

 of its hurtling fragments, shattering the strongest work 

 oi human hands as easily as the frailest. Such a blow 

 might well be sensible over half a continent, and give 

 rise to undulations, which, unseen and unfelt, might 

 wend their way round the globe. 



THE EVOLUTION OF SIMPLE SOCIETIES. 



By Professor Alfred C. IlAnnoN, m.a., sc.d., f.r.s. 



IV.— THE BEGINNING OF AGRICULTURE. 



The origin of agriculture is lost in the mists of antiquity. 

 We know that in Neolithic times in Europe, eight kinds 

 of cereals were cultivated, besides flax, peas, poppies, 

 apples, pcai-s, bull ace-plums, etc. ; at the same time 

 various animals were domesticated. Among these were 

 hoi-ses, short-hornod oxen, horned sheep, goats, two 

 breeds of pigs, and dogs. Professor W. Boyd Dawkins 

 says that evidence goes to show that these animals were 

 not domesticated in Europe, but probably in the central 

 plateau of Asia. He also thinks that agriculture arose 

 in the south and east of Europe and spread gradually 

 to the centre, north, and west. However this may have 

 been, the growth of agriculture was in all likelihood 

 slow, and some peoples do not take at all kindly to it. 



Wo have already seen that a hunting population is 

 often very averse to even the slight amount of work 

 that agriculture requires in a tropical country. The 

 same holds good, as a rule, for pastoral communities. 

 In all cases a powerful constraint is necessary to force 

 these peoples into uncongenial employment. Fate is 

 stronger than will, and at various periods, in different 

 climes, hunters and herders have been forced to till 

 the soil. 



In the New World there were no domestic animals 

 in pre-Columbian times. Owing to the absence of the 

 horse, the bison that roamed in countless numbers over 

 the prairies could not be herded. On foot the intrepid 

 Redskins tracked and slew with bow and arrow the big 

 cattle they could not tame. When the horse arrived, 

 the Redskins, or Amerinds (as our American colleagues 

 now term them and all other autocthonous tribes), were 

 too inveterate hunters to change their mode of life. 



Over a considerable portion of America maize was 

 cultivated from unknown antiquity, and other food 

 plants and cotton were grown in suitable localities. It 

 is doubtful whether the ancient civilizatipns of Mexico 

 and Peru could have arisen had it not been for the 

 cultivation of maize. Certainly they would have been 

 impossible but for agriculture. 



In the West Pacific, again, there are no domestic 

 animals to speak of, no horses, cattle, sheep nor goats ; 

 the natives are fishers and hunters who have taken to 

 a simple kind of agriculture, or it might more correctly, 

 perhaps, be termed, horticulture, as no cereals are grown, 

 not even rice, but only root crops such as yams, sweet 

 potatoes, and taro ; the banana is the only fruit tree 

 that is cultivated in the true sense of the term, though 

 the cocoanut, areca palm, bread-fruit, and a few other 

 trees are grown. To take one example, the naked 

 savages of Kiwai Island, at the mouth of the Fly River 

 in British New Guinea, cultivate thirty-six varieties of 

 bananas, twenty kinds of yams, and ten sorts of sweet 

 potatoes, all of which have distinct names. Their only 

 domestic animals are the pig and the dingo. 



We have seen in the previous article how the deserts 

 of Arabia and Sahara predispose the populations to 

 commerce through the insufficiency of pasturage, and 

 the organisationof the tribe educates the chiefs in the 

 exercise of government. 



The passage of these populations to a sedentary life 

 is effected in the oases. These islands of vegetation in 

 the desert are artificial. Created by man they disappear 

 if not maintained by constant care. The creation of an 

 oasis is a particularly difficult enterprise. In this 



