264 T. 8. Hunt on Lithology. 
dinary conditions, or perhaps in some cases derived from volcanic 
ash or voleanic mud. As the other extreme of this series of 
rocks we may notice that dolerites often assume a trachytic form 
—the trachy-dolerites already mentioned—or constitute the lavas 
from modern volcanos, Me 
mong the compound rocks which are related to the preceding 
group by the presence of augite may be noticed nepheline-doler 
ite, in which nepheline replaces the feldspar ; and analcimite, a 
variety into which analcime enters in large amount. Scapolite 
also in some cases replaces feldspar, and forms with green pyrox- 
€ne, a peculiar aggregate associated with the Laurentian lime- 
Stones. Leucite enters as an important element in some doler- 
ites, and even replaces wholly the feldspathic element, giving 
rise to what has been called leucitophyre or leucilite. es 
[Leucite is generally regarded as an exclusively volcanic mine 
eral, but according to Fournet, it occurs like other feldspars i 
mineral veins, forming the gangue of certain auriferous veins 10 
. 
Mexico, (G@éologie Lyonnaise, p. 261). According to Scheerer 
posed by Brongniart as a synonym for black po hyry, (mn 
Von Buch employed the name of melaphyre as synony? 
with augite-porphyry, in which he was followed by Dill, 
