Haworth on the Archcean Geology of Missouri. 371 
here in Missouri an illustration of the gradual transition from a 
holocrystalline, coarse-grained rock through the fine-grained 
ones into those which originally were vitrophyres ?" If the 
field relations strongly corroborate the evidence obtained from 
the hand specimens it will add greatly to the probabilities in 
favor of the correctness of an affirmative answer. Let us see 
what the facts are. 
There are two important points however which should con- 
stantly be kept in mind while considering this question. 1°. The 
present elevations may, and probably do, differ from those which 
obtained during the period of solidification of the rock masses. 
The time has been so long that surface erosion and oscillations 
may have somewhat changed the original contour. 2''. The 
surface of this original eruptive mass during the period of solid- 
ification very probably was quite uneven. It is the distance 
below this original surface at which any given rock mass solid- 
ified that should determine its structure, and not necessarily its 
relation to the present surface. 
It is therefore manifest that in certain cases there may be ap- 
parent i-eversions of the rule that the farther below the surface 
a rock exists the more coarsely cr^^stalline it is. Such cases are 
not lacking. Specimen number 214, from the very summit of 
Shepard mountain is more highly crystalline than number 204, 
which came from a point in the valley 600 feet below. But 
there are many reason for believing number 204 was in a valley 
of the erupted material and that this valley has not been eroded 
as much as has the top of Shepard mountain, therefore number 
214 probably cooled faither below the surface than did number 
304. 
Now it is an interesting fact that all the granite exposures 
are on comparatively low ground, with porphyry hills near by; 
and also that generally there is good evidence of extensive ero- 
sion from the surfaces of the granite beds. Thus we find them 
along the valley of the St. Francois, the largest stream in the 
district; and along the lower portion of Stout's creek. The 
Graniteville quarries, it is true, are not located on a stream of 
any great size, but they are in a valley with high porphyiy hills 
almost all around. Passing back from the streams wc find that 
whenever granite is exposed it is a fine grained variety, and in 
