372 WHITMAN CROSS 
regarded as a nearly constant mixture of certain elements and 
as characterized by a certain structure. Species were supposed 
to be much more numerous than the unimportant transition 
types—‘‘roches du passage.” 
The rock species was determined almost solely on minera- 
logical grounds. Geological origin and occurrence were used 
merely as appropriate elements in the description of the species 
—stating its habitat, so to speak. | 
Species were grouped in genera according to the state of 
aggregation, as explained below. Orders were based upon the 
power of the eye to distinguish the character of the rock. The 
most important of the still larger groups, the family, was formed 
in most cases upon the predominant mineral present, and the fami- 
lies were grouped upon an indefinite chemical basis, in four 
classes, namely: 
Class 1. Earthy rocks (roches terreuses). 
Class 2. Saline or acid non-metalliferous rocks (Roches salines ou acidi- 
féres non métalliques). 
Class 3. Metalliferous rocks (Roches métalliféres). 
Class 4. Combustible non-metallic rocks (Roches combustibles non 
métalliques. 
Predominance of one mineral constituent, the quantitative 
factor applied to form families, the most important of divisions 
aside from the species, was assumed to mean: (1) more than 
half where two constituents were concerned; (2) more than one- 
third where three constituents were present,and so on. In com- 
plex rocks it was naturally difficult of application and was 
almost impossible in aphanitic rocks. Moreover, it was not 
adhered to strictly, as pointed out by D’Orbigny in regard to 
basalt, which was referred to the pyroxenic family although 
feldspar might really predominate over pyroxene. “As D’Or- 
bigny naively remarks: ‘But it is this latter substance which 
gives its character to the rock’’ (Mais' c’est cette derniere sub- 
stance qui donne son caractére a la roche). 
The elaborate system of Cordier may be illustrated by the 
following section, giving the subdivisions within the feldspathic 
family: 
