4 Journal of the Mitchell Society [ May 
canic rocks along the eastern border of North America. These 
rocks are analogous to the halleflintas and eurites of Southern 
Sweden, described as volcanic rocks by Nordenskjold. They 
would also correspond to Hunt’s pre-Cambrian petro-silex rocks, 
called by him the Arvonian, being below his Huronian. 
“The hornstones have every appearance of being acid feldspar- 
quartz rocks, and will probably be found, on further study, to 
belong to the class of apo -rhyolites, a term introduced by Miss 
Bascom to denote a devitrified rhyolite. Emmons 1 describes 
the type very well under the head of quartzite. They resemble 
perfectly crypto-crystalline quartz, and on weathering present an 
earthy, yellowish surface. The color of the fresh rock is drab, 
bluish to almost black; translucent on edges; fracture flat con- 
choidal; sometimes banded, showing flow structure, etc.” On 
pages 41 and 42 of the same report the following is quoted from 
Dr. Williams’ 2 article: “ ‘In a drive from Sanford to Chapel Hill 
an abundance of the most typical ancient lavas, mostly of the 
acid type, was encountered’ ” - - - - “ ‘Another locality in 
the volcanic belt was visited on Morgan’s run, about 2 miles 
south of Chapel Hill. Here are to be seen admirable exposures 
of volcanic flow and breccias with finer tuff deposits, which have 
been extensively sheared into slates by dynamic agency.’ ” The 
above is repeated verbatim by the same author 3 the same year 
(1896) in an article entitled, “Some Late Views of the So-called 
Taconic and Huronian Rocks in Central North Carolina.” 
The tenor of those parts of Nitze’s paper just quoted referring 
to the origin of the fine grained quartz rocks, seems to be that 
these rocks are closely connected with the ancient surface lava 
flows which are so common throughout the region. He states 
that none of them were examined miscroscopically, but suggests 
that the hornstones will probably be found to be apo-rhyolites. 
The references to the work of Dr. Williams and Dr. Bascom on the 
structure and devitrification of ancient acid lavas show that Nitze 
1 Geological Report, Midland Comities of N. C,, New York, 1856, p. 51. 
2 Journal of Geology, vol. 2, 1894, pp. 1-31. 
3 This journal, vol. 13, Part Second, July- Dec. , 1896, pp. 53-72. 
