1058 The American Naturalist. [December, 
miles of rocks exposed along the eastern side of South Mountain as 
ancient lavas. “These rocks,” he continued, “have been heretofore 
often described by geologists, but have been considered to be of sedi- 
mentary origin. To any one, however, familiar with the products of 
recent volcanic regions the proofs of their lava character are convin- 
cing. In spite of their great age and complete recrystallization they 
still retain the minutest details of their original structures. Even 
under the microscope they are hardly to be distinguished from recent 
glassy or half-glassy rocks from the Yellowstone Park or from southern 
Italy. In chemical composition also they show surprisingly little 
change. 
These old volcanic rocks present two sharply contrasted types. One 
is basic in composition and agrees in all respects with our recent 
basalts, the other is acid in composition and belongs to the group of 
lavas called porphyry, or rhyolite. In South Mountain the rocks of 
the latter class, which occupy about twice as much space as the basic 
ones, have been called slates, while their green, basic contemporaries 
have been known as chlorite schists. The discovery of such extensive 
lava fields in such wonderful preservation and so near at hand was 
unexpected, and deserves attention on account of its local interest. 
The age of the lavas and their relations to the sandstone of the 
mountain, which Mr. Walcott has recently shown to be of the oldest 
known fossil-bearing horizon, was then explained. Attention was 
called to the fact that, as in most volcanic regions, large deposits of 
fragmental material occur (breccias, ashes, etc.), which have heretofore 
been considered as sedimentary beds. A large map of South Moun- 
tain, on a scale of three miles to the inch, was exhibited to show the 
distribution of all these rocks. Numerous specimens of the rocks 
themselves were also shown. Many of the porphyries are of great 
beauty, and are capable of extensive application in the arts, especially 
when polished for purposes of interior decoration.” 
Prof. E. D. Cope’s paper was on The Fauna of the Blanco Epoch. 
Prof. Cope said in part: “The formation known as the Blanco has 
been discovered by Texan geologists and forms a part of the Great 
Staked Plain. I visited this region,” he said, “the geology of which — 
has been so much misunderstood, last spring, and obtained numerous 
fossil remains, from which I have determined fifteen species of verte- 
brata, all new to science and constituting a fauna intermediate between 
two previously known faunæ, and filling an important gap in the his- 
tory of life on this continent. The species found included two tortoises, 
one bird, one sloth, three mastodons, one peccary, three horses, one 
