Queries and Answers. 489 



air will, I think, ordinarily, be found injurious. Thus, in 

 granite, which has a kind of parallelogrammatic cleavage, 

 water introduces itself into the fissures, and the result, in a 

 sharp frost, will be a disintegration of the rocks en masse ; 

 and, if the felspar be predominant in the composition of the 

 granite, it will be subject to a rapid decomposition. The 

 morvine of some of the Chamouni and Allee Blanche glaciers 

 is composed of a white granite, being chiefly composed of 

 quartz and felspar, with a little chlorite. The sand and gravel 

 at the edge of these glaciers appears far more the result of 

 decomposition than attrition. All finely foliated rocks, slates, 

 &c, are liable to injury from frost or wet weather. The road 

 of the Simplon, on the Italian side, is in some parts dangerous 

 in, or after, wet weather, on account of the rocks of slate con- 

 tinually falling from the overhanging mountains above : this, 

 however, is mere disintegration, not decomposition. Not so 

 with the breccias of central Switzerland. The rock of Righi 

 is composed of pebbles of different kinds, joined by a red 

 argillaceous gluten. When this rock has not been exposed 

 to the air, it is very hard : you may almost as easily break the 

 pebbles as detach them from their matrix ; but, when exposed 

 for a few years to wind and weather, the matrix becomes soft, 

 and the pebbles may be easily detached. I was struck with 

 the difference between this rock and a breccia at Epinal, in 

 France, where the matrix was a red sandstone, like that of the 

 Cathedral of Basle. Here, though the rock had every ap- 

 pearance of having been long exposed to the air, it was as 

 hard as iron ; and it was utterly impossible to detach any of 

 the pebbles from the bed : it was difficult even to break the 

 rock at all. I cannot positively state that the gluten in these 

 sandstones is calcareous, but I suppose it to have been so. 

 Compact calcareous rock, as far as I remember, appears to 

 be subject to no injury from the weather. Many churches in 

 Italy, and almost the whole cities of Venice and Genoa, are 

 built of very fine marble ; and the perfection of the delicate 

 carvings, however aged, is most remarkable. I remember a 

 church, near Pavia, coated with the finest and most expensive 

 marbles: a range of beautifully sculptured medallions running 

 round its base, though old, were as distinct and fine in their 

 execution as if they had just come out of the sculptor's studio. 

 If, therefore, the gluten of the sandstone be either calcareous 

 or siliceous, it will naturally produce the effect above alluded 

 to, though it is certainly singular that the stone should be soft 

 when first quarried. Sandstone is a rock in which you seldom 

 see many cracks or fissures in the strata : they are generally 

 continuous and solid. Now, there may be a certain degree 



