My purpose in calling attention to this point is simply to suggest that the proper way to begin the study of minerals and rocks with children is to first familiarize them with the elements of which they are composed. The most important thing to be known about any mineral is its chemical composition; and when a child is told that a mineral—corundum, for example—is composed of oxygen and aluminum, he should have a distinct conception of the properties of each of those elements, for otherwise corundum is for him a mere compound of names. It is very important, too, if the pupil has not already studied chemistry, that he should be led to some comprehension of the nature of chemical union and of the difference between a chemical compound and a mechanical mixture. For this purpose a few simple experiments (the details of which would be out of place here) with the more common and familiar elements will be sufficient. Mrs. Richard’s “First Lessons in Minerals” should be introduced here. Mineralogical Composition of Rocks. The fourteen elements named above are combined to form about fifty minerals with which the student of geology should be acquainted; but not more than one-half of these are of the first importance. It is desired to lay especial emphasis upon the importance of a perfect familiarity with these few common minerals. There is nothing else in the whole range of geology so easily acquired which is at the same time so valuable; for it is entirely impossible to comprehend the definitions of rocks, or to recognize rocks certainly and scientifically, unless we are acquainted with their constituent minerals. With one or two exceptions, these common rock-forming minerals may be easily distinguished by their physical characters alone, so that their certain recognition is a matter of the simplest observation, and entirely within the capacity of young children. Furthermore, being common, specimens of these minerals are very easily obtained, so that there is no reason why teachers should not here adopt the best method and place a specimen of each mineral in the hands of each pupil. Typical examples, large enough to show the characteristics well, ought not to cost, on the average, over two cents apiece. A MINERAL is an inorganic body having theoretically a definite chemical composition, and usually a regular geometric form. THE PRINCIPAL CHARACTERISTICS OF MINERALS.—These may be grouped under the following general heads:— (1) _Composition_, (2) _Crystalline form_, (3) _Hardness_, (4) _Specific gravity_, (5) _Lustre_, (6) _Color and Streak_.