PDF - Wallace Online

150 NATURAL SELECTION vnits purpose so effectually. Nothing but a mind could have soexactly adapted the slopes of the channels, their capacity, andfrequency, to the nature of the soil and the quantity of therainfall. Again, he would see special adaptation to the wantsof man, in broad, quiet, navigable rivers flowing through fertileplains that support a large population, while the rocky streamsand mountain torrents were confined to those sterile regionssuitable only for a small population of shepherds and herdsmen.He would listen with incredulity to the geologist whoassured him that the adaptation and adjustment he so admiredwas an inevitable result of the action of general laws ;thatthe rains and rivers, aided by subterranean forces, hadmodelled the country, had formed the hills and valleys, hadscooped out the river beds and levelled the plains and it;would only be after much patient observation and study,after having watched the minute changes produced year byyear, and multiplying them by thousands and ten thousands,after visiting the various regions of the earth and seeing thechanges everywhere going on, and the unmistakable signs ofgreater changes in past times, that he could be made tounderstand that the surface of the earth, however beautifuland harmonious itmay appear, is strictly due in every detailto the action of forces which are demonstrably self-adjusting.Moreover, when he had sufficiently extended his inquiries,he would find that every evil effect which he would imaginemust be the result of non-adjustment does somewhere or otheroccur, only it is not always evil. Looking on a fertile valley,he would " perhaps say: If the channel of this river were notwell adjusted if for a few miles it sloped the wrong waythe water could not escape, and all this luxuriant valley, full ofhuman beings, would become a waste of waters." Well, thereare hundreds of such cases. Every lake is a valley "wastedby water," and in some cases (as the Dead Sea) it is a positiveevil, a blot upon the harmony and adaptation of the surfaceof the earth. Again, he might say "If rain did not fallhere, but the clouds passed over us to some other regions,this verdant and highly cultivated plain would become adesert." And there are such deserts over large portions ofthe earth, which abundant rains would convert into pleasantdwelling-places for man. Or he might observe some great