Editoiial Com?ne?it. 375 
Eruptivgesteine des Kristianiagebietes" (1894- 1898), al- 
though so recently issued, have become classics in petrology. 
The subject of the last five lectures of the course just 
completed at the Johns Hopkins University shows that Dr. 
Brogger has entered yet another field of inquiry. On Wed- 
nesday, April 25th and on the following Thursday professor 
Brogger lectured before the students of the geological de- 
partment of Johns Hopkins University and visiting geolo- 
gists, upon "The Principles of a genetic classification of the 
Igneous Rocks." These lectures embraced a historical re- 
view of the classification of igneous rocks, a criticism of the 
present artificial classification and the suggestion of princi- 
ples upon which a natural classification should be based. 
The fundamental principle of Dr. Brogger's classification 
is the geological relationship of igneous rocks, to be deter- 
mined by geological investigation. This principle gives him 
"his three genetic classes: abyssal, hypabyssal, and effusive, 
which are well known through his published writings ("Die 
Eruptivgesteine des Kristianiagebietes" Part I). Chemical 
composition was made a basis of further grouping and in- 
teresting detailed classification was introduced. These lec- 
tures were illustrated by a complete series of the remarkable 
igneous rocks from the region of Christiania. 
( I ) The essexyte series was represented by abyssal, hyp- 
abyssal and effusive types, with both chemical and structu- 
ral peripheral facies. In the same way was illustrated; 
(II a) The Augite Syenyte series. 
(II b) Nepheline Syenyte series. 
(II c) Pulaskyte series. 
(II d) Mica Syenyte series. 
(III) Akeryte series. 
(IV) Nordmark\'te series. 
(V) Soda Granite series. 
(VI aj Granite series. 
(VI b) Rapakiwi granite series. 
(VII) Diabase and Proterobase. 
Dr. Brogger generously leaves this fine collection in this 
country. 
The succeeding five lectures were upon "The Late Geo- 
logical History, as shown by changes of level and climate 
