234 THE PHYSICAL MANIFESTATIONS OF WEATHEEING 



eaten awa^, more like slags or cinders than blocks of limestone. 

 The ridges between Harrington Sound and Castle Harbor are a 

 good example of this. It is like a rockery of the most irregular 

 and fantastic style, and there seems to be something specially 

 productive in the soil ; for every crack and crevice is filled with 

 the most luxuriant vegetation, mossing over the stones and train- 

 ing up as tier upon tier of climbers, clinging to the trees and 

 rocks. Frequently the percolation of hardening matter, from 

 some cause or other, only affects certain parts of a mass of rock, 

 leaving spaces occupied by free sand. There seems to be little 

 doubt that it is by the clearing out of the sand from such 

 spaces, either by the action of running fresh water or by that 

 of the sea, that those remarkable caves are formed which add 

 so much to the interest of the Bermudas/' 



A form of weathering due to similar causes, but productive 

 of results much more regular in arrangement, is shown in 

 Fig. 4, PL 22, from a block of weathered sandstone in the 

 National Museum. The original joints through which the 

 waters filtered are easily recognized in the sharp straight lines 

 running diagonally across the specimen. Blocks of fine shale 

 and argillite, in their incipient stages of weathering, often show 

 concentric bands of varying color, due to the oxidizing effect 

 of water percolating inward from all sides of the natural joints 

 as shown in Fig. 3, PL 22. 



In stratified rocks there is, as a rule, a lack of homogeneity, 

 certain layers being more porous than others, or containing 

 mineral constituents more susceptible to the attacking forces. 

 Such rocks, therefore, weather unevenly, and give rise to ex- 

 ceedingly ragged contours. The finely fissile schists standing 

 nearly on edge along the coast of Casco Bay, in Maine, under 

 the combined influence of wave and atmospheric action, weather 

 into peculiarly fantastic forms resembling nothing more than 

 piles of old lumber in which the multitudinous channels formed 

 by boring coleopterous larvae have become irregularly enlarged 

 by decay. (See Fig. 1, PL 20.) The numerous quartz veins by 

 which these schists are traversed stand out in bold relief until 

 no longer supported by the matrix, when they fall to the beach, 

 where, together with fragments of the schist, tney are gradually 

 reduced to pebbles and fine sand. 



(4) Weathering influenced by Mineral Composition*— Al- 

 though the sodaJime feldspars yield to the decomposing agen- 



