94 THE NATURE STUDY COURSE. 



formers may be picked up in many school sections. Nearly 

 every granitoid boulder, examples of which are scattered all 

 over the country except in the sedimentary soil (e.g., around 

 Lake St. Clair) will show quartz, feldspar (usually reddish in 

 color) and mica (small glistening flaky particles). Try to 

 obtain in some way, samples of these rocks for use in a lesson 

 on the origin of soils. 



Frost as a soil-former is sometimes shown experimentally as 

 follows : — Take two or three pieces of porous stone and a piece 

 of brick j wash them clean and then soak them for several 

 hours in water. They imbibe better if not entirely covered 

 with the water. Put each piece in a clean saucer and set them 

 outside overnight or for two or three nights. In accounting 

 for the particles of the rock that may be found in the saucers 

 the pupils will discover how Jack Frost works as a soil-maker. 

 This experiment has to be done in the winter, the weather 

 should be so cold at the time that the water will freeze before 

 it has time to dry out. 



Classes of Soils. — Returning to the hole, obtain samples of 

 each of the kinds of soil observed ; a quart tin-can or a gem 

 jar full of each will suffice for co-operative study. To a small 

 cupful of the subsoil add an equal volume of water. Stir 

 it very thoroughly and pour off all but the heaviest layer into 

 another vessel ; add some more water, stir and pour off and 

 repeat until you have only the coarse gravel left. What 

 has been poured off should be saved, and after the sediment 

 has settled and the nearly clear surplus water is poured 

 off and thrown away a process of separation is gone through 

 similar to the first until only the sand is left. The residue 

 is silt and clay, which may be obtained by settling and 

 siphoning off the nearly clear water. The three samples 

 may then be dried and weighed or measured. This operation 

 gives a mechanical analysis of the soil by sedimentation. 

 Which ever constituent predominates gives its name to the 



