S49 LI BMAIHE SAIIS OCI CAI Te BG 375 
and, if not wholly original, one must suspect the dominant 
influence of Naumann’s views. Its main outlines are as follows: 
Three families of rocks are recognized : 
I. Igneous rocks. 
II. Aqueous rocks. 
III. Metamorphic rocks. 
Igneous rocks are divided into three groups: 
1, Granitic (in the sense of granular). 
2. Porphyritic. 
3. Volcanic. 
Aqueous rocks into three groups: 
1. Chemical deposits. 
2. Mechanical deposits. 
3. Carbonaceous rocks, of vegetable origin. 
Metamorphic rocks into three groups: 
1. Crystalline schists. 
2. Those of chemical origin. 
3. Those of mechanical origin. 
It will be seen that this system is in its outline wonderfully 
like many of recent years in its logical use of factors in con- 
struction, and in the order of their application. In further sub- 
division, finally producing species, Coquand was less fortunate, 
being governed still by the mineralogical idea too closely. 
Probably he was much less fitted for the descriptive task than 
Cordier, who doubtless surpassed him in intimate knowledge of 
the detailed characters of rocks as cabinet specimens; but he 
certainly possessed a logical mind, and grasped far better than 
his contemporaries the relations of petrography to geology. 
Archibald Getkie, 1872.—Turning to the literature of other 
countries during this period, it is evident that systematic petrog- 
raphy was developed as a science almost wholly through the 
labors of workers in Germany and France. Prior to the micro- 
scopical era, soon to be considered, practically no special stu- 
dents of this subject appeared in either Great Britain, America, 
or in other countries. Aside from the discussions of geologists, 
like De la Beche, already mentioned, there was in Great Britain 
no important contribution after the time of Macculloch. The 
