LOWEST, OR OLD RED, SANDSTONE. 223 



most common for the conglomerate to be the lowest: 

 being sometimes however uppermost, while they also 

 occasionally alternate, through a whole deposit, and 

 further, sometimes occupy different parts of the same 

 bed, which thus undergoes a lateral change of texture. 

 Single fragments of large size occasionally also intrude; 

 and the presence of rounded masses does not exclude 

 that of angular ones, as the two sometimes occur to- 

 gether. In the conglomerates as in the sandstones, 

 the induration is so various that the fragments seem 

 at times to be barely in contact : whence the mass is 

 easily disintegrated by a slight force, or by the wea- 

 ther ; while, at others, they are cemented by indurated 

 clay, sometimes with calcareous carbonat, or by crys- 

 talline quartz, so as to present every degree of indu- 

 ration : often emulating that of quartz rock, when fine, 

 and of granite, when coarse; and also presenting, in 

 the former case, similar compact, uniform, and splin- 

 tery fractures. And, respecting the structure, I must 

 also observe, that a cuboidal or analogous division of 

 the strata often confers on this sandstone the phy- 

 siognomy of granite, when the angles have been 

 rounded by exposure to the weather. 



If the theory of this deposit, so important in the 

 philosophy of geology, ought now to be apparent, it 

 requires a few additional words; since geologists have 

 mistaken more than one essential point respecting it. 

 That it has often been a deposit beneath water, 

 formed in the same manner as the later sandstones, 

 is obvious ; but the facts will not allow me to admit 

 that every example, or all the parts of any one, have 

 been produced in this simple and gradual manner. The 

 enormous masses of the conglomerates, with their pe- 

 culiar internal characters, their uncertain and often 

 singular positions, their repetitions, and other circum- 



