16 GEKERAL CHARACTERISTICS OF MINERALS. 



and when this fluid finally ceases to circulate, it dies and 

 soon decays. 



Minerals, on the contrary, have no such nourishing fluid. 

 The smallest particle is as perfect as the mountain mass. 

 They increase in size only by additions to the surface from 

 some external source. The deposit of salt forming in an 

 evaporating brine, has layer after layer of particles added to 

 it, and by this mode of accumulation, its thickness is at- 

 tained. 



Beds of an ore of iron, called bog iron-ore, are some- 

 times said to grow. They do in fact increase in extent. 

 Rills of water running from the hills wash out the iron in 

 the rocks they pass over, decomposing and altering the condi- 

 tion of the ore, and carry it to low marshy grounds. Here the 

 water becomes stagnant, and gradually the iron is deposited 

 This bog ore, as the name implies, is found mostly in low 

 marshy places, and often contains nuts, leaves, and sticks, 

 changed to iron ore. The increase here is obviously by ex- 

 ternal additions. 



In limestone caverns, and about certain lakes and streams, 

 the water contains much carbonate of lime. As it evapo- 

 rates, layer after layer of the lime is deposited, till thick 

 beds are sometimes formed. In caverns, the water comes 

 dripping through the roof, drop by drop, and each drop 

 as it dries, deposits a little carbonate of lime. At first it 

 forms but a mere wart on the surface ; but it gradually 

 lengthens, till it becomes a long tapering cylinder, and 

 sometimes the pendant cylinder, or stalactite, as it is called, 

 reaches the floor of the cave, and forms a column several 

 feet in diameter. 



It thus appears that minerals increase, or enlarge, by ac- 

 cretion, or additions to the surface only. They decrease, 

 or the surface is worn away, by the action of running water 

 and other agents. When they decay, as sometimes happens 

 from contact with air and moisture, or some other cause, the 

 change begins with the surface, and results in producing 

 one or more different minerals. The line of demarkation, 

 therefore, between living beings, and minerals or inorganic 

 matter, is strongly drawn. 



Characters of Minerals. In pursuing the subject of min- 



What are the different modes of increase in the animate and mineral 

 kingdoms? Mention examples of increase in mineral substances, and 

 explain the mode. 



