140 Geology of Upper Illinois. 



The construction of a canal-basin, at the termination of the ca- 

 nal, with an area of five and a half acres, whose bottom is to be 

 considerably elevated above the present level of the bottom-lands, 

 serves to render this division of the undertaking also, very expen- 

 sive. The cost of the entire canal, as estimated according to the 

 report of the commissioners, is $8,654,337 ; but it is admitted that 

 the estimate is too low, it being generally believed that the work 

 will not be brought to a state of completion under ten millions 

 of dollars. 



The geology of the chief portion of the route above described, 

 is exceedingly simple and uniform, the great rock formation of 

 the country being the magnesia?! limestone ; at least, this is the 

 rock from the commencement of the canal, (four miles from Chi- 

 cago,) nearly to the mouth of the Kankakee, It also reappears 

 west of the Fox river, as will presently be pointed out, and enjoys 

 a wide distribution probably throughout the whole of Upper Illi- 

 nois and Wisconsin. A good opportunity for examining its char- 

 acter occurs near Chicago, where the excavations have already 

 been commenced. It here rises quite to the surface of the prairie. 

 It is imperfectly stratified, with an evident dip of 10° or 15° to the 

 north-west. Its color is light grayish white, with a frequent 

 shade of yellow. It is compact in texture, and often slightly cel- 

 lular or cavernous — a peculiarity which seems to be connected, 

 for the most part, with the profusion of organic remains existing 

 among its materials at the period of its formation. The follow- 

 ing is a brief list of the fossils which fell under my observation 

 at this locality : two species of Orthocera, a Turbo (one and a 

 half inches in diameter) with a depressed spire ; a large species 

 of Pectunculus ? ; a Terehratula, (with very prominent ribs, and 

 but few in number;) two species of ylwmomVes ; a Caryophyl- 

 lia, and a Favosites* Some of the beds are wanting in fossils, 

 and occasionally the rock puts on a shistose or slaty structure, in 

 Avhich case it forms a valuable flagging-stone, which is already 

 employed to some extent in Chicago. 



The same rock reappears in the bed of the Des Plaines, twelve 

 miles from Chicago, on the road to Juliet, as well as near the sur- 



* Several of these species I am persuaded are new ; but I defer a particular de- 

 scription of them until I shall obtain an additional supply of specimens, promised 

 me by Dr. Brainard, of Chicago. 



