ee 
J. D. Dana on the characters distinguishing Kinds of Rocks. 337 
“dolerytes” of subsequent time, have shown that material of 
essentially the same chemical composition, has been ejected in 
all geological ages, as has been well urged by Allport and 
others. The analyses might be cited; but this is not necessary, 
since in mineral composition typical diabase and doleryte are 
admitted to be identical. 
€ facts show, consequently, that orthoclase rocks, or ortho- 
clase and oligoclase, have been erupted from Paleozoic time 
Cency in the feldspar, and some glass at times among the erys- 
talline grains ; but nothing that has any geological weight. 
While then it may be well to retain the names of trachyte and 
felsyte, on account of the obvious external differences and the 
