98 GENERAL REMARKS ON THE 



rare indeed to find any bed which, however fine in its 

 predominant character, does not somewhere contain larger 

 fragments. With the exception above noticed, there is also 

 no connexion between the structure and the relative place 

 of the strata in the order of superposition ; as the summits 

 of the highest mountains, equally with the lower beds of 

 which they are formed, present extensive masses of the 

 conglomerate. The fragments of these, it must however 

 be remarked, are rarely if ever so entire as in those beds 

 which repose immediately on the gneiss; almost always 

 bearing, in a greater or less degree, the marks of 

 attrition. 



It is scarcely necessary now to say that this sandstone 

 must be ranked in the class of primary rocks. On no 

 other view can the preceding facts be explained, notwith- 

 standing the occasional points of resemblance which it 

 presents to those of the secondary division. It must 

 therefore be considered as a red primary sandstone ; and 

 that it is not even the latest of the primary strata, is evi- 

 dent from the preceding history of its connexions. 



No objection need arise with respect to the use of the 

 term primary, as applied to a rock composed of the re- 

 united fragments of former rocks. That term has here, 

 as on other occasions throughout this work, been sub- 

 stituted for the word primitive, and is purely relative; 

 implying nothing theoretical respecting the origin of any 

 order of rocks, whether stratified or amorphous. Nor 

 is this sandstone a solitary example of the mechanical 

 recomposition found among rocks of the primary 

 division. The instances of this structure occurring in 

 the quartz rock of Jura and the associated islands, are 

 equally remarkable; and there are indeed striking ana- 

 logies between that series and the present in many im- 

 portant particulars. The obvious differences, in fact, 

 frequently consist in little else than colour ; the essential 

 one in these two cases being the presence or absence 

 of felspar, whence, in the red sandstone, that colour 



