The Geoloylc llisforij of Missouri. — WinsJoir. 85 
rainable. The only considerable exposure at present is the 
small patch on Pilot Knob. Possibl}^ rocks of the same for- 
mation are represented under the surrounding Paleozoic beds ; 
of this, however, there is no positive evidence, excepting, per- 
haps, in the record of a deep drill hole put down at Kaytown, 
■south of Kansas City. Here the base of the Paleozoic rocks 
was reached at a depth of 2,430 ft., and below this 36 ft. of 
crystalline rocks were penetrated. A specimen of this core 
examined by the writer, is a highly micacious schist, com- 
posed almost entirely of black mica. It is different from any 
rocks found in the Archean of the southeast and is more like 
rock referred to the Algonkian elsewhere. A drill hole at the 
St. Louis insane asylum 3,600 ft. deep, one at Carthage about 
2,000 ft. deep and one near Sullivan, Franklin county, about 
1,200 ft. deep, all reached crystalline rock. In the first, 
the rock is reported by Prof. Broadhead to have been granite; 
in the second, Mr. J. D. Robertson determined the specimens 
to be porphyry ; in the third, drillings examined by the writer 
consisted of pink feldspar and quartz like those of the Ar- 
chean granites. These last results, therefore, are opposed to 
the existence of Algonkian rocks at the respective localities, 
though such may have existed there in the past and have 
since been removed. 
I'he Cambrian Period. — During the Cambrian period, Mis- 
souri was probably a land surface, at least in large part. This 
conclusion is reached : first, because there are either only a 
very limited thickness or no rocks of this age in the state; 
iind second, because there is evidence of a very great erosion 
between the Algonkian era and the Silurian period. During 
this interval all but the small Pilot Knob patch of Algonkian 
beds were entirely removed and the underlying Archean gran- 
ites and porphyries were deeply trenched. It is to this date 
that we must assign the original sculpturing of the hills and 
valleys of southeastern Missouri, around and between which 
the Silurian limestones are now spread. To have eroded this 
great massof resistant Algonkian and A*"chean rocks must cer- 
tainly have taken a long period, even geologically considered. 
Possibly, this elevation and erosion may have begun well back 
in the Algonkian time and have continued through the ('am- 
brian. This would make the maintenance of the conditions 
