482 Home Nature- Study Course. 



How Stone Flour is Made by Weathering. 



On your trip going or returning, I hope you may find some shale 

 rock. This will be the softest rock of which you know and contains no 

 grit. The action of the frost, sun and rain has softened and torn it in 

 pieces, which you will often find in piles of flakes. The most probable 

 places where such rock may be found will be in the cut of the road or 

 where the stream curves at the base of a cliff. Some of your pupils may 

 be made to understand that the rock crumbs have been broken from the 

 walls by the power of Jack Frost and his helpers, the sun and storms. 

 Jack's work may seem to proceed slowly, but it goes on continually and 

 with no idle moments. Fill a paper bag with the rock crumbs and take 

 them back to the school room. At a time when the weather does not 

 permit of field excursions, the pupils may make as much artificial clay 

 in a comparatively short time as would keep Jack busy for several years. 

 Yet it would be well to impress on the minds of the children that while 

 Jack may seem to do work slowly, a hundred tons to him is no more than 

 an ounce to first and second graders. It is well to say to them, also, that 

 soil has undergone many other changes since it was originally pulverized ; 

 but this subject is not adaptable to small children. 



The most expeditious way to pulverize the shale is in a mortar and 

 when finely crushed add enough water to make the rock flour as stiff 

 as putty. Let your children mould some of it into marbles and small 

 plates and let them dry. To another lot of artificially made clay add 

 about one-half sand and when wet mould more marbles and let them 

 dry. This last lot will not have the stick-together quality that had the 

 first. The sand has made the difference, and why? For a third experi- 

 ment, let the children mould some more marbles — at least try to — with 

 only a small quantity of water added to the crushed shale and they will 

 quickly realize how difficult it will be because there has not been enough 



water used to make the clay sticky. The lesson 

 sought is to impress on the minds of the children the 

 fact that if they have a garden on clay soil and they 

 hoe or spade it when wet the seed-bed will be lumpy 

 and not soft and fine such as seeds like best. If they 

 wait until the clay garden is partly dry cultivation 

 will then make it "mealy " and will give a downy bed 

 of ease for seeds or plants. 



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