468 Canadian Record of Science. 



three series — the Granitic, the Granitc-Porphyritic, and 

 the Lamprophyritic Dyke rocks. These three series have 

 been arranged in horizontal rows — separated merely by 

 spacing, not by lines. 



The division of the Volcanic rocks into older and newer is 

 still retained, although but little stress is laid upon it, hence 

 in the table these two divisions are separated by an inter- 

 rupted line. In many cases rocks of these two classes can- 

 not be distinguished from one another, but in other cases 

 they present differences (generally due to partial alter- 

 ation) by which they are characterized. As geologists 

 have been accustomed to give special names to rocks pos- 

 sessing these special characters, the distinction may for the 

 present at least be retained as convenient. Thus although 

 Liparite may be identical in all essential respects with 

 Quartz Porphyry, geologists are not yet prepared to aban- 

 don either term. Both rocks have certain characters which 

 renders a special name advantageous, although these char- 

 acters have little or no value for purposes of classification. 



In constructing such a table it becomes very difficult to 

 decide just how much detail in classification should be in- 

 cluded and how much left out. If too little is put in, the 

 table is of no value to any but those desiring the most 

 elementary knowledge of the subject, while too much detail 

 renders the table too complicated and cumbersome. I have 

 therefore made it a general rule to omit in the subordinate 

 classification names based merely on structural differences. 

 e.g., ^sevadite, Granophyre, etc., and to employ only those 

 based on the actual differences of composition. One or two 

 exceptions have been made in the case of rocks which seemed 

 of especial importance. In this way, many names which 

 would serve only to confuse the student are omitted, while 

 most of those of real importance are retained. The attempt 

 has also been made by employing several kinds of type to 

 bring out prominently the chief subdivisions and more 

 important rocks, and to classify the others in a general 

 way according to their importance. In a few cases also, 

 where a rock is merely a variety of those immediately pre- 



