PART L] CULTURAL 101 



parts of the world, the better they have been pleased. The 

 familiar burnt brick of the South of England, and the slag and 

 painted coke of the northern coal districts, are better than these. 



It is needless to point out in detail what rocks are suitable 

 for alpine gardens in the different parts of Britain ; a walk in 

 the country will show the rocks, and a glance at any geological 

 map will tell their names. 



The second rule not to be departed from is one not so easy 

 to adhere to, but quite as important as the last, viz.: The 

 form of your rocks should be that which in Nature is assumed 

 by the particular kind of rock of which it is composed. In 

 order to appreciate the amount of observation which this rule 

 renders necessary, we must consider what are the various 

 agencies which together bring about on rocks the result 

 which geologists know by the name of " weathering." Nature's 

 mode of making her rocks weather-beaten requires such an 

 amount of time, that we cannot attempt to imitate her in that 

 respect ; but if we cannot use her means, we can copy her 

 results. Now, the weathering of a rock depends, before all 

 things, on the structure of that rock, on its composition, and on 

 the manner in which it is exposed to sun, rain, frost, wind, and 

 the atmosphere itself, which are the great weathering and rock- 

 carving agents. On many rocks water acts mechanically only ; 

 or, to be more accurate, its power of dissolving some rocks, such 

 as quartz, is so limited, even when, as is almost always the case, 

 it is charged with carbonic acid, that it is inappreciable, and 

 may for practical purposes be left out of the reckoning. On a 

 great mass of quartzite rock, for instance, the effect of rain 

 would be of this kind. It could scarcely dissolve any of it 

 away ; but it would insinuate itself into every crevice and 

 fissure and crack with which such hard rocks abound near the 

 surface, and thence, by the help of frost, it blasts to shivers, 

 winter after winter, layer after layer of this tough rock, just in 

 the same manner as it bursts the water-pipes of our houses. By 

 observation it is found that every rock affects a more or less 

 peculiar kind of fracture; so that in bursting splinters from 

 them, as has just been shown, the lines of fissure are not 



