Jbrming the basis of' Old Red Sandstone. S^7 



substance has been deposited by hot springs, they must have 

 been very large and very numerous, and it would be astonishing 

 should no remains of them be still visible. None of those which 

 I saw were either saline, or warm, or incrusting. The nearest 

 warm spring is that of Bourbon TArchambault, and it does not 

 form siliceous deposits. 



The sandstones which contain this gelatinous quartz must 

 have been deposited at the same time with itself, for they are in- 

 timately mixed. The gelatinous part always contains rounded 

 grains of quartz, and it is rare that the sandstones have not this 

 jelly, which serves as a cement to it, although it is only in small 

 quantity ; and there is a transition from the one to the other by 

 a change in the proportions of the rounded grains, and of the dis^ 

 solved portion. 



The variety of sandstone which abounds most in gelatinous 

 silica, is formed of grains of hyaline and milk-white quartz, 

 rounded, and of a small size ; some grains of opal also are seen 

 in it, but there is no felspar or kaolin. When the silica is in 

 the nectic state, it is difficult to determine whether there be kao- 

 lin or not, from the mutual resemblance which these two white 

 and friable substances possess. Another variety of sandstone, 

 is, in a great measure, formed of grains of hyaline quartz ; some 

 scales of mica and spots of red oxides of iron are also perceived 

 in it. The red spots are seen to increase in size and number ; 

 they are formed of a siliceous paste, coloured with tritoxide of 

 iron. The red colour at length predominates, and the mass be- 

 comes entirely of that tint ; a multitude of small grains of quartz 

 and of gelatinous spots are, however, seen in it. 



These sandstones are supported by conglomerates composed 

 of blocks of quartz, granite and micaslate. These conglome- 

 rates rest immediately upon the primitive formations. Above 

 the red-sandstones there occur strata of sandstone and bitumi- 

 nous slate, with impressions of ferns and junci, containing beds 

 of black coal and iron-ore. They have the same direction and 

 inclination as the coal-sandstones which they support. No rock 

 of volcanic origin is found in all these formations. It is, there- 

 fore, in an intermediate deposit, which might be referred to the 

 old red-sandstone, or the lower beds of a coal-formation, that 



Y 2 



