98 GEOLOGY OF ILLINOIS. 



These were noticed to lie thickest where boggy and springy places were 

 met with, surrounded by rougher and more rolling land. The boulders 

 are all from the metamorphic regions of the north, and consist of granite, 

 gneiss, hornblende, trap, and some other varieties, with their various 

 combinations. Across the whole northern part of the county these 

 boulders were noticed in a greater or less abundance, associated with 

 clays and sometimes clayey sands. Across the central part of the county 

 the coarse gravel beds, unstratifted hard-pan, and partially stratified 

 clays make up the surface covering of the rocks. Under these, all over 

 this region, laminated clays rest upon the indurated rocks below. Some 

 of the gravel beds northwest of Caledonia are almost a mile long, and 

 several feet deep. They are made up of materials very much rounded 

 and abraided ; are partially stratified ; the gravel is of all sizes, inter- 

 mingled with clean sand. A low drift hill of gravelly clay lies close to 

 Belvidere, on which the court house stands. In the banks of the Kish- 

 waukee, a short distance below the bridge between the north and south 

 parts of the city, on the north side of the stream, are outcrops of 

 the bank of tenacious potters' clay, before referred to. It runs under 

 at least a part of the city, and in one place borings for some public 

 work showed it to be some seventy feet in thickness. At another locality 

 some workmen were sinking a well. After going through this deposit, 

 which there was much thinner, water rushed into the well so fast that 

 the men could hardly get out in safety. 



In many places I heard of the traditional nuggets of copper that pre- 

 viously had been found among the gravel and boulders, but I could not 

 succeed in finding any myself. Over this whole region, in connection 

 with my observations upon the drift, I watched closely in order that I 

 might detect indications of glacial action ; but I am forced somewhat 

 reluctantly to admit that atmospheric and chemical agencies and aque- 

 ous forces probably explain most of the phenomena connected with these 

 superficial deposits. In the morraiue-like hillocks of Ogle county 

 glacial action, I think, is more manifest. 



The Cincinnati Shales. As already intimated, the shaly rocks of 

 this deposit underly nearly all that part of the county south of the 

 Kishwaukee. Coon creek doubtless cuts down to the Galena ; but all the 

 prairie ridges show the outcroppings of the former rocks, although 

 worked exposures are rare. In fact there is but two good stone quarries 

 in Boone county: one in the Cincinnati shales, five or six miles south of 

 Belvidere, and one in the Galena limestone three or four miles north- 

 west of the city. The former of these is opened in the brow of a low 

 hill. A few feet of clay and subsoil is stripped from the surface of the 

 shingly rocks. The formation is quarried into about eighteen feet in 

 depth, and great quantities of stone have been removed and hauled for 



