April II, 1872] 



NATURE 



467 



now stand at various levels on the steep slopes bounding 

 narrow valleys" (p. 329). "This mud, which is very hard 

 and solid when dry, becomes traversed by vertical cracks 

 after having- been moistened by rain, and then dried by 

 the sun. Those portions of the surface which are pro- 

 tected from the direct downward action of the rain by 

 a stone or erratic block, become gradually detached 

 and isolated." " The lower part of some of these 

 ancient columns . . . has acquired new capping 

 stones by the wearing out at the surface of blocks origi- 

 nally buried at great depths" (p. 332). 



There they stand, a measure of the mass of drift that 

 has been carried away by rain, as workmen sometimes 

 leave a pillar of brickeanh or clay here and there over a 

 field to measure the depth of the earth they have removed. 



They remind us also of the small pedestals of lime- 

 stone which large boulders have sometimes preserved for 

 themselves in the same way, and of the ice pillars where 

 the thick stone cap had to keep off the sun instead of the 

 rain. 



By the courtesy of the publisher we are able to subjoin 

 a sketch given by our author of an isolated stone-capped 

 column seen by him near Viesch (Fig. l). 



In considering the action of rivers, Sir Charles notices 

 how the clearing of forests increases the erosive power of 

 the rain water. Speaking of a ravine in Georgia, he says, 



"before the land was cleared it had no existence, but 

 when the trees of the forest were cut down, cracks three 

 feet di?ep were caused by the sun's heat in the clay, and 

 during the rains a sudden rush of water through the prin- 

 cipal crack deepened it at its lower extremity, from whence 

 the excavating power worked backwards till, in the course 

 of twenty years, a chasm measuring no less than 55ft. in 

 depth, 300 yards in length, and varying in width from 20ft. 

 to 180ft., was the result" (p. 339). 



In many parts of France the destruction of the woods 

 has proved a source of very great injury, as they caught 

 the rain and parted with it slowly, tine roots all the while 

 protecting the soil. But, now that the woods have been 

 cut down' the water runs off at once, scouring away the 

 earth from the slopes of the hills, and in the valleys 

 causing sudden floods which sweep everything before 

 them 



In America it is especially interesting to watch the 

 effect produced by man in this way upon climate and 

 water supply. 



We are shown the power of rivers, especially in flood, 

 to tear away and transport to long distances the broken 

 masses they find in their path. The glacier and ice- 

 sheet, too, are for ever grinding and wearing the solid 

 rocks away. But space will not allow us to give more 

 than one other example, and we will select the formation 



Fig. 2.— Granite Rocks to the Sc 



of a pinnacle of solid rock by the action of the sea, which 

 it will be interesting to compare with the column of in- 

 durated mud, of which we have given a sketch above. 



In considering the waste of sea chffs, our author quotes 

 Dr. Hibbert's account of a passage forced by the waves 

 through rocks of hard porphyry, where the sea tears large 

 masses of stone from the sides and forces them along, 

 sometimes to a distance of no less than 180 ft, and adds ; 

 —"Such devastation cannot be incessantly committed 

 for thousands of years without dividing islands, until they 

 become at last mere clusters of rocks, the last shreds of 

 masses once continuous. To this state many appear to 

 have been reduced, and innumerable fantastic iorms are 

 assumed by rocks adjoining these islands, to which the 

 name of Drongs is applied, as it is to those of similar 

 shape in ' Feroe'" (p. 512). (Fig. 2.) 



By such illustrations we are taught how ceaseless and 

 how powerful are the destroying agencies of nature. But 

 where is all this matter transported to.? Sir Charles 

 Lyell takes us out into mid- ocean, where he points out to 

 us the icebergs carrying their load far and wide, and 

 dropping it here and there over the sea bottom in warmer 

 climes. On the shingle beach we see it travelling, and 

 in the deep blue sea, says Dr. Tyndall, we see finely- 

 divided matter still travelling on. With our author we 

 examine the deltas of the great rivers, the Nile, the 

 Ganges, and the Mississippi ; and he shows us that some 



th of KiLLSWicK Ness, Shetland. 



of the material is for a time arrested there. He tells us 

 of the most recent discoveries in mid-Atlantic, where a 

 chalky mud is being deposited over an area wider than 

 that over which the ancient chalk sea has been traced ; 

 where swarms of little creatures live and die, and drop 

 their tiny shells in such countless millions that the mud 

 is in a great measure made up of them ; where they 



Sow 

 The dust of continents to be, 



and give to us the explanation of the conditions under 

 which that great deposit known as the Chalk was forme^l 

 Sir Charles Lyell refers to this in the following passage : "A 

 fallacy which has helped to perpetuate the doctrine that the 

 operations of water were on a difterent and grander scale 

 in ancient times, is founded on the indefinite areas over 

 which homogeneous deposits were supposed to extend. 

 No modern sedimentary strata, it was said, equally iden- 

 tical in mineral character and fossil contents, can be 

 traced continuously from one quarter of the globe to 

 another. But the first propagators of these opinions 

 were very slightly acquainted with the inconstancy in 

 mineral composition of the ancient formations, and 

 equally so of the wide spaces over which the same kind 

 of sediment is now actually distributed by rivers and 

 currents in the course of centuries. The persistency of 

 character in the older series was e.xaggerated ; its extreme 

 variability in the newer was assumed without proof. In 



