CONGLOMERATES 31 



are by far the oldest rocks known within the limits of the state 

 of Missouri — much more ancient than any of the great series 

 of sediments found in the region. There is now not the slight- 

 est doubt that these old crystallines are, for the most part, 

 truly igneous ; that they were once in a molten state, but long 

 since cooled and became solidified. 



In the present connection, further reference to the crystal- 

 lines is perhaps unnecessary, yet they are of importance strati- 

 graphically, in being the nucleus around which a great series 

 of Paleozoic sediments accuumlated in this part of the Ameri- 

 can continent. 



ALGONKIAN FORMATIONS. 



The succession of strata in the Ozark region of Missouri 

 is but little understood as yet. There is certainly a great body 

 of massive crystallines which are manifestly much more an- 

 cient than any of the sedimentaries which everywhere overlie 

 them, and of which brief mention has just been made. Along 

 with the granites are porphyries ; then lie thick beds of con- 

 glomerate made up of porphyry fragments. Associated with 

 these are certain slates and beds of iron ore. 



The conglomerates are more or less perfectly bedded. 

 Those occurring on Pilot Knob have been referred to by Van 

 Hise and others as probably representing the Algonkian of 

 the Lake Superior region and elsewhere. There are doubtless 

 other conglomeratic deposits in the same district, which are 

 contemporaneous with the Pilot Knob rocks ; and on the other 

 hand, many of the conglomerates were probably formed at the 

 same time as the limestones and sandstones which surround 

 the crystalline peaks. 



That these truly eruptive rocks are more ancient than the 

 surrounding sedimentary beds is shown chiefly by: 



( 1 ) An entire absence of contact metamorphism in the 

 associated strata. 



( 2 ) Presence of angular fragments of the crystallines in 

 the sedimentary beds abutting the igneous elevations. 



( 3 ) Presence of crystalline breccias between the hori- 

 zontal limestone and massive rocks. 



