538 Murchison 's Silurian System. 



very small pebble of quartz. Below, the conglomerate usu- 

 ally becomes finer, and passes into a pure sandstone of brown- 

 ish and occasionally gosling green, and deep red colours; 

 other beds are much spotted with green blotches on a dark 

 red ground. Where roads are contiguous this sandstone is 

 quarried for troughs, cider presses, and building purposes, 

 and some of the lower layers of this division are so fissile 

 and fine grained as to allow of their being quarried for flag- 

 stones and grindstones. These rocks are distinguished from 

 the next division of the system by the absence of calcareous 

 beds.* In some of the ridges where the lower beds pass 

 into cornstone and marl, thin layers filled with fragments 

 of carbonised vegetable matter have been found, but never 

 in so perfect a form as to resemble fossil plants. These 

 appearances have induced ill-advised speculators to drive 

 galleries into mountains of this rock in search of coal. 



These sandstones assume a very ancient aspect. " We 

 must not, however," says Mr. Murchison, "judge of the 

 antiquity of rocks by their mineral aspect, nor even by their 

 lithological structure ; for, as I shall have occasion to show, 

 there are many portions of the old red sandstone undistin- 

 guishable in these respects from the oldest grey wacke, 

 whilst strata of the underlying Silurian system, formerly 

 termed greywacke, so far from assuming an air of higher 

 antiquity, in numberless cases, and over very large areas, re- 

 semble closely some of the younger secondary deposits." 



The reader will be desirous to know how far this descrip- 

 tion of the upper division of the old red sandstone in South 

 Wales applies to any of the rocks of India. We have 



* Very rarely, Mr. Murchison remarks; where this upper division of 

 the old red sandstone is much expanded, it occasionally contains thin 

 courses of mottled, red, and green, very impure limestone, not to be dis- 

 tinguished from some of the least calcareous beds of cornstone. In 

 one of these beds Mr. Murchison discovered the scale of a large fish 

 not vet described. 



