1904J Nature Study — No. -50. 



199 



Besides these mechanical changes of granite constituents, 

 chemical changes also take place. Felspar contains, among- 

 other things, sodium, calcium and potassium. These dissolved 

 out furnish the salts of the ocean. The sodium furnishes the 

 common salt, which under favorable conditions is laid down as 

 beds of rock salt. Teach this in connection with salt mines and 

 salt springs of the geography lesson. The calcium, united with 

 carbonic acid, gives limestone, which in solution is washed into 

 the sea, where sea animals use it to make their shells. These 

 animals die, and the shells collect on the sea bottom as ooze, 

 shell-limestone, etc.. according to the kind of animal. This shell 

 mass may re-dissolve and be re-deposited as crystalline limestone 

 cemented by its own material. Under right conditions of heat 

 and pressure, marble is one of the forms of limestone thus 

 originated. 



You should now have in your school collection all the rocks 

 and minerals above named— granite, sandstone, quartzite, shale, 

 slate, marble, coral, shell limestone, compact limestone, as well 

 as dolomite and gypsum, which are naturally studied with lime- 

 stone. Samples of sand and clay of different textures, with the 

 rocks they came from, are necessary to teach the origin of soil. 



It would be advisable, too, to make a mineral map of your 

 province by taking a large table, marking off an outline map of 

 the province, and covering it with rocks distributed as they are 

 in the province itself. Mountains should be piled up with their 

 proper rocks. Place a piece of iron ore for each iron mine, but 

 do not place, say, hematite where limonite is mined. Indicate the 

 locality of other minerals, mines and quarries in the same way. 

 A glance at such a map gives the child a good understanding of 

 the mineral wealth of his province, the association of minerals, 

 the reason for location of centres of industry, and a knowledge of 

 the farming lands, for the soil depends largely on the kind of 

 rocks and their durability. On such a map do gold and coal 

 occur in similar rocks ? What about coal and limestone ? What 

 are the associate rocks of coal? Ask similar questions with 

 reference to other minerals. The boy has learned now that rocks 

 break up to form soils. Does he find in the field or the river-bed 

 rocks different from those of the surrounding country ? How did 



