CHAP. xxi. CHANGES OF SUBSTANCE. 367 



ing causes. There have been changes from the action of 

 heat, and changes without heat. To understand changes 

 from the effects of heat, I suppose we must go to Ice- 

 land. To understand changes without heat, we have 

 only to look around us. 



" Last summer, I went one evening down to Murkle 

 Bay. At one corner of the shore, at the west side of the 

 bay, was a pile of sand. It had been accumulated, and 

 lay on the land in a mass, blown up gradually in old 

 times no one knows how old. The sand was mixed 

 with broken shells and small pebbles. Water had been 

 finding its way through and amongst the sand. The 

 shells had partly decayed. The lime [of the shells] had 

 set, and bound the sand and pebbles, in some places, 

 into a solid mass. In fact, it had became a stone a 

 rock. It required a smart blow of a hammer to break 

 it. And in much the same way many a deposit of sand 

 has thus become sandstone or freestone. 



" Some years ago, I saw in the hands of Dr. Robert 

 Chambers of Edinburgh a piece of siliceous quartzite. 

 It had been taken from one of the metamorphic hills of 

 Sutherland. It had evidently at one time been a mass 

 of loose sand. In fact, it still resembled sandstone 

 more than typical quartz. How it became a mass of 

 flinty stone I know not; but evidently not from the 

 effects of heat. 



" Some years ago there was a great talk of liquid 

 silica, or liquid flint flint, in fact, as thin as water. 

 Many public buildings, it was said, had been built of a 

 material so loose that under weather influences they were 



