44 IOWA ACADEMY OF SCIENCES. 



look deeply and well into the mountains and vales, trace out the tortuous 

 water courses as they have etched their tangled way through oftimes seem- 

 ingly impenetrable measures and softer strata; to survey the streams and 

 behold there the narrow chasms or gorges with mural escarpments which 

 occur in irregular succession. Thus will the hidden scenery, t-he beauty 

 of the landscape, sculptured by natui-e, be revealed. 



The ci-ystalline rocks of Missouri are for the most part porphyries and 

 granites and are confined exclusively to the southeastern portion of the state. 

 They occur southeastward, almost to the northern limit of the earthquake or 

 sunken area of Missouri; they occur westward more than one hundred miles 

 from the Mississippi, the neai'est known outcrop to this stream lying less 

 than twenty miles distant. If a quadrilateral with township lines be here 

 drawn to include all exposures of Archtean rocks, it would contain about 

 four hundred square miles; a circle drawn to surround these exposures 

 would have a diameter of more than eighty miles. Yet the surface of either 

 of these figures which is occupied by the crystallines is less than one-tenth 

 of the total enclosure. Occurring in ten counties, they are more abund- 

 antly exposed in Iron, Saint Francois, Madison, Wayne and Reynolds coun- 

 ties. In the others the exposures are scattering and not unfrequently quite 

 isolated. In fact, some of these isolated outcrops being quite low, not much, 

 if an J, above the general level, are found, perhaps, only by chance. These 

 crystalline rocks are the oldest in the state. They stood long prior to the 

 forming of the latter sedimentary rocks. After standing for ages as 

 parts of the continental body, they now appear with sandstones and lime- 

 stones originating from the degradation of this continent surrounding them. 



The Ai'cha3an hills often occur in groups each separated by divides or val- 

 leys of the same formation or they occur as individual and grouped 

 points separated by Lower Silurian or Cambrian beds. The distance from 

 Archrean, across Cambrian, to Archrean, may be a few feet or twenty 

 or twenty-five miles and the length or broadest diameter of the continuous 

 crystalline areas varies to about this extent, though the great majority of 

 these are much smaller than the upper extreme. 



Made up almost wholly of the crystallines and other hard rock and void 

 of any glacial drift, southeast Missouri abounds in excellent exposures of the 

 beds there existing. Presenting such varieties of rock, frequently in occur- 

 rences somewhat singular, the attention of the geologist is ever attracted. 

 Problem after problem has arisen and been solved, yet to-day the field is 

 oew; many problems of great importance stand out for solution. 



In addition to the porphyries and granites here present there are large 

 areas of sandstone, limestone, or limestone capped with chert masses and 

 fragments. Each of these is represented by a type of topography entirely 

 distinct from that of any the other formations. The valleys of the sedimen- 

 tax-y rocks do not resemble the valleys of the crystallines more than the hills 

 of the former the mountains of the other. Of course in some places the type 

 may be less chai'acteristic than in others. 



To the east of the southern limit of the crystalline region the elevation of 

 the Mississippi river is approximately 300 feet above sea level. The highest 

 ascertained altitude of the Archtean hills is 1,800 feet whilst the greatest ele- 

 vation of the Cambrian hills is about 1,700 feet. Of the former the porphyry 

 hills are the highest; of the latter the chert-capped limestone ridges are more 

 elevated, consequently more conspicuous. 



