SVSTEMA TIC. PETROGRAPHY, 345 
classification of volcanic rocks accompanying his memoir was 
limited to the few surface lavas then known and the tuffs and 
ashes. He had the idea that either feldspar or pyroxene pre- 
dominated in all cases, and hence the first division was into 
feldspathic and pyroxenic rocks. Texture was the main prop- 
erty applied for further subdivision. 
Folin. Macculloch, 1522.—The third decade of the century 
witnessed the publication of several important essays in rock 
classification. .The first of these was by John Macculloch, and 
was entitled Geological Classification of Rocks, with Descriptive 
Synopses, Comprising the Elements of Practical Geology, issued in 
London, 1822. Macculloch’s work is called ‘‘a classification of 
rocks,”’ but it is really a classification of rock formations, as we 
should now express it. It is an attempt at stratigraphic geology 
without recourse to fossils. Its foundation was a knowledge, 
which was very thorough for the time, of the rocks of a limited 
area, and the assumption that the same rocks must, in general, 
occur in all parts of the world in the same sequence and rela- 
tions as in the British Isles. In discussing the basis of his 
scheme he says: 
In considering the different plans on which a classification of rocks 
might be constructed, he (the author) was, without hesitation, led to adopt 
one founded on the geological relations and positions of rocks innature . 
the basis of the arrangement is virtually the same as that adopted by Werner. 
Macculloch thought that all rocks might be placed in a few 
groups, distinguished by certain prevailing mineral characters. 
It will be further seen [he says| that these different groups are also in a 
great measure distinguished in nature by certain general or geological rela- 
tions, more or less constant and perfect. 
The arrangements according to mineral characters and geo- 
logical relations were believed to coincide. 
The attempt to use fossils as criteria of the age of rock for- 
mations, which was then being made by the Germans, did not 
appeal to Macculloch. He is said to have been jealous of the 
Journal de Physique, 1815-1816. Both memoir and table of classification were 
reprinted by D’Orbigny in 1868, in his work Description des roches, etc., which gave 
the system of Cordier as elaborated at the time of his death, in 1861. 
