SYSTEMATIC PETROGRAPE Y 347 
OCCASIONAL ROCKS. 
Jasper. Gypsum. 
Siliceous schist. Conglomerate rocks. 
Chert. Veinstones. 
Appendix. 
Volcanic rocks, Alluvia. 
Clay, marl, sand. Lignite. 
Coal. Peat. 
If we examine this table, it is seen that Macculloch was not 
able to carry out consistently the application of the factors 
adopted. This is most conspicuously the case with the ‘over- 
lying (and venous) rocks” placed in the unstratified division of 
the secondary class. These overlying rocks were, in fact, recog- 
nized as later than the secondary rocks in many cases. They 
are mainly what we should call intrusive igneous rocks, found 
cutting other rocks, and of the real age of which Macculloch 
confessed that he had little evidence. He was ignorant of the 
composition of aphanitic or felsitic rocks, and they receive no 
consistent treatment at his hands. 
Macculloch is credited with having been a keen observer 
and with having made truly great contributions to stratigraphic 
geology. But he does not appear to have conceived of the dis- 
tinction between a geological formation and a rock. There are 
in his book many phrases, such as the title of the work itself, 
and statements scattered through it, which are couched in the 
language of today, but have very different significance at this 
time. It is interesting to apply many of his remarks concern- 
ing the condition of the systematic science of rocks, as under- 
stood by him, to the petrography of today. 
Karl Cesar von Leonhard, 1823.—In 1823 appeared a truly 
epoch-making work, the Charakteristik der Felsarten by Karl 
Cesar von Leonhard, professor at the University of Heidelberg. 
This is, in fact, the first fairly consistent treatise upon rocks. 
It is founded upon an exceptionally accurate knowledge of the 
objects classified, and with advanced ideas as to the true rela- 
tions between geognosy proper and the descriptive science of 
