28 NATURE STUDY REVIEW [9:1— Jan., 191:? 



The feldspathic rocks are those that contain feldspar. The 

 ferro-magnesian rocks are those that contain a considerable 

 amount of the minerals that contain iron and magnesium. They 

 are as follows : hornblende, pyroxene, biotite, and olivine. One 

 or more of these minerals is nearly always found in the feld- 

 spathic rocks but in small amounts, less than one-fourth of the 

 rock usually. Since the color of a rock is the color of the mix- 

 tures of the various minerals it contains, it is readily seen that 

 the rocks that contain very much of these minerals would be 

 dark. The same reasoning applies to the feldspathic rocks. 



The above table is not only a general classification of igneous 

 rocks but is also a determinative table. Thus a light colored 

 rock which has grains that can be distinctly seen and which con- 

 tains feldspar and quartz, all the grains being about the same 

 size, or non-porphyritic, is a granite. It is a very good plan 

 to memorize this table then it is always ready for use. 



Hygiene as Nature-Study 



F. M. Gregg. 

 Peru (Nehr.) State Normal. 

 IV. A Study of the Mouth and Its Uses. 

 Next in magnitude to the proportion of people afifected by 

 germ diseases comes the proportion of people who are affected by 

 the ills to which flesh is heir in consequence of bad feeding. In 

 more exact diction, flesh is not ''heir" to either of these causes 

 of human illness, except in so far as there is a figurative heritage 

 of customs and environment, for diseases due to the two general 

 causes named are in large degree, if not wholly, within the con- 

 trol of the individual. The matter of feeding is so largely sub- 

 ject to modification through habit that it is manifestly a part of 

 the school's duty to supplement the efforts of the home in securing 

 right habits early in the life of the pupil, with respect to eating. 

 Fourth and fifth grade pupils are none too young upon whom 

 to operate for the end desired in feeding practices. Malnutrition, 

 alleged to characterize one pupil in four in America, is in part, 

 at least, traceable to undesirable habits of eating. This may in 

 turn be traced to various causes, among them to decayed teeth 

 and rapid eating. 



(a) THE NATURE-STUDY APPROACH. 



1. A study of the mouth cavity. — (a) As an important pre- 



