CHAP. IV.] THE VOYAGE HOME. 213 



you find a few trailing spikes of Nassauma serpens., or a few 

 heads of the graceful drooping chrysanthemum -like Chabrcea 

 su(meolens. 



These stone rivers are looked upon with great wonder by 

 the shifting population of the Falklands, and they are shown 

 to visitors with many strange speculations as to their mode of 

 formation. Their origin seems, how^ever, to be obvious and 

 simple enough, and on that account their study is all the more 

 instructive, for they form an extreme case of a phenomenon 

 which is of wide occurrence, and whose consequences are, I be- 

 lieve, very much underrated. 



There can be no doubt that the blocks of quartzite in the 

 valleys are derived from the bands of quartzite in the ridges 

 above, for they correspond with them in every respect ; the 

 difficulty is to account for their flowing down the valley, for 

 the slope from the ridge to the valley is often not more than 

 six to eight degrees, and the slope of the valley itself only two 

 or three, in either case much too low to cause blocks of that 

 form either to slide or to roll down. 



The process appears to be this : The beds of quartzite are 

 of very different hardness ; some are soft, passing into a crum- 

 bling sandstone, while others are so hard as to yield but little 

 to ordinary weathering. The softer bands are worn away in 

 process of time, and the compact quartzites are left as long pro- 

 jecting ridges along the crests and flanks of the hill - ranges. 

 When the process of the disintegration of the softer beds has 

 gone on for some time, the support of their adjacent beds is 

 taken away from the denuded quartzites, and they give way in 

 the direction of the joints, and the fragments fall over upon 

 the gentle slopes of the hill-side. The vegetation soon covers 

 the fallen fragments, and usually near the sloping outcrops of 

 the hard quartz, a slight inequality only in the surface of the 

 turf indicates that the loose blocks are imbedded beneath it. 

 Once imbedded in the vegetable soil, a number of causes tend 



