78 GEOLOGY OF ILLINOIS. 



A vast amount of carbon is contained in the black shales of this 

 group. Specimens taken from near Savanna, and from the Beers Tom- 

 linsou farm, are almost as black as caimel coal, and burn with an 

 oily bright flame for a considerable time. Misled by this, some capital 

 has been expended at the latter place in boring for coal, and nothing 

 but experience will convince those engaged that such a search is useless. 



One of our citizens also succeeded in extracting some oil, which he 

 pronounced petroleum, out of similar specimens. When the great oil 

 excitement arose in the country, an oil company was formed here, and 

 but for the advice of the geologists, this company would now be spend- 

 ing its money in a vain effort to strike oil. The geologist of Iowa, Prof. 

 WHITNEY, estimates that the carbon of these rocks, if gathered into 

 one strata, would form a bed twenty-five feet thick. 



Whence came this mass of combustible matter in these old Silurian 

 rocks ? No geologist, to my knowledge, has undertaken to answer this 

 question. Is it of organic origin, the remains of an ancient vegetation '? 

 Is it the result of animate life, the coral ? HALL'S Iowa report states 

 that no trace of vegetation has as yet been observed in the widely dis- 

 tributed shales of this group, except a few traces of fucoids in the Utica 

 slates of New York. This makes him doubt the vegetable origin of this 

 bituminous matter. In this county, however, we have discovered fu- 

 coids woven all over the tops of some of the strata in this formation. 

 May it not be that a condition of things similar to that in the Carbonif- 

 erous eras, existed over the broad basin in which these shales were de- 

 posited ? The vegetation consisted of the lowest orders, such as would 

 decay and leave few traces of their existence. The disorganized re- 

 mains would alone remain in the form of carbon or coaly shale. The 

 day may come when this substance, whatever it is, will be of economic 

 value, for light or even fuel. With this brief notice, we must dismiss 

 for the present this very interesting question. 



This formation is prolific of fossils. Countless remains, with an oc- 

 casional perfect specimen of the splendid large trilobite, the Asaphus 

 gigas, are the most noticeable. Orthis occidentalis and 0. testudinaria 

 abound. Some of these shales are covered with beautifully marked 

 deudrites. Fucoids are also found. Orthoceratites and a large Lituites 

 have been found in it, together with numerous other fossils. 



The Niagara Limestone. This is Owen's "pentamerus beds" of the 

 Upper Magnesia u limestone. It is next in order above the group just 

 considered. The traveler on the Upper Mississippi must have been 

 struck with its bold and picturesque appearance as he passed between 

 Fulton City and Dubuque. Now the bluffs sweep down to the water's 

 edge ; now they trend off in a semi-circular direction, as if for the site 

 of a colossal amphitheater. Their bases indicate the gentle slopes of 



