296 Haworth on the Archc^an Geology of Missouri. 
(c) Strjtcttirc of the granites. 
The granites from Graniteville, Syenite, Stout's creek, and the 
St. Francois river are moderately coarse-grained, of a pink color 
which varies considerably in shade, and are generally mottled 
with biotite or hornblende. At Graniteville and Syenite very 
extensive quarries are worked, which produce grades of granite 
equal in appearance to the New England granites. In localities 
different from the ones named the granites have a finer texture, 
and grade off into the porjDhyries. 
It may well be said that in but few instances do we find gran- 
ites which do not in some degree possess a structure approach- 
ing the porphyritic. That from Graniteville shows it the least. 
Those along Stout's creek and the St. Francois have it much 
more developed. The hornblende, when present, is always 
idiomorphic, and the feldsjDar, biotite and quartz are to a con- 
siderable extent. The well formed crystals of quartz in num- 
ber 303 has already been mentioned. The feldsj^ar enlarge- 
ments have an important bearing here. They show unmis- 
takably that there were two distinct periods of solidification, 
and consequently that the only difference between the structure 
of the granites and the overlying porphyries is in the character 
of the product of the second period of solidification. 
As we pass back from the low ground vv'e invariably find the 
texture of the granite becoming more fine, and in every respect 
more closely resembling the porphyries and felsytes. The 
structure of the rocks intermediate between the granites and 
the poi'phyries can best be considered after the porphyries have 
been described. 
(i/) Class ijicat ion of the granites. 
As has already been stated the granites are all very similar 
in mineralogical composition. There are but three different 
varieties which are sufficiently distinct to be given separate 
viames. The first of these is composed wholly of feldspar and 
quartz, excepting the few unimportant accessory minerals 
which may occur in all granites. From its intimate associa- 
tions with biotite granite we must look upon it as being a facies 
of the latter. The third variety has a small amount of horn- 
blende, but by no means a sufficient amount to bring it under 
