Colour of the Rocks in the Lake District. 63 



are varieties of clay-slate, more or less modified by metamor- 

 phic agencies. Their colour, as exhibited by a fresh fracture, 

 is grey of different shades, owing chiefly to the presence of a 

 minute portion of carbonaceous matter. Accordingly, when 

 exposed to the action of an open fire, the grey hue is destroyed. 

 Its colour is changed to shades, commonly light, of red or 

 yellow, from the combustion of the carbonaceous matter, and 

 the conversion of some protoxide of iron, — an oxide seldom 

 entirely absent from the composition of these rocks, — into 

 peroxide. And the effect of weathering — of long exposure to 

 the atmosphere, — is similar, where the circumstances are such 

 as to permit of its being witnessed without interference of 

 adventitious causes, — as in the instance of rocks subjected 

 to the action of torrents when the streams they skirt are 

 flooded, and that so frequently as to prevent the growth of 

 the lower order of plants on their surface. 



Secondly^ Of the nature of the discolouring matter. When 

 abraded and placed under the microscope, it is found to be 

 composed in most instances of granular matter like that of 

 soot, and of fibres and cells like those afforded by the lower 

 order of vegetables, such as the mucors, lichens, and mosses 

 in a state of change, analogous probably to that by which 

 peat is formed from the same class of plants. Further, 

 ignited in the open air, the colouring matter burns, and is 

 consumed, leaving only a very little ash. 



Considering the composition of the rocks of the district, as 

 adverted to, and these results, are we not justified in the 

 conclusion that the discolouration is adventitious ; and, more- 

 over, that it is occasioned partly by a substance resembling 

 soot, and partly by vegetable matter of a peaty character. 



The source of the latter matter is easily found, the tendency 

 to form peat being always to be observed in this climate 

 wherever the local circumstances favour, such as moderate 

 moisture, water more or less stagnant, shade, and lowness of 

 atmospheric temperature. The rocks, the surface of which are 

 most discoloured, — are of the darkest hues, — are so situated 

 as to be under the influence of these circumstances, especially 

 the " watery rocks," an expressive term of our great poet — 

 rocks over which water oozing from the ground above, com- 



