202 



SCIENCE, 



[Vol. XXII. No. 558 



when lighting is done by electricity and heating by gas 

 the whole aspect of our towns will be changed for the bet- 

 ter. We have, however, no wide experience in this coun- 

 try to which to point as an object lesson in such a direc- 

 tion. In the United States gaseous fuel has been much 

 more freely applied, and there are, I understand, instances 

 in which coal has been almost entirely superseded by nat- 

 ural gas. If any of your contributors could say how far 

 this is the case and give some idea of the effect which such 

 a change has produced on the air of the locality and on 

 the aspect of the town in question, a signal service 

 would be rendered and a distinct advance would be made 

 in the direction of banishing the fog demon once and for 

 all. 



THE UTICA SHALE IN STEPHENSON COUNTY, 

 ILLINOIS. 



BY OSCAE H. HEKSHEr, FEEEPORT, ILL. 



In the various reports of the Illinois Geological Survey 

 all the strata from the top of the Galena Limestone to the 

 base of the Niagara have been classed together under the 

 term Cincinnati Group. So far as northwestern Illinois 

 is concerned this was probably the only classification pos- 

 sible from the limited data at hand. As a general thing 

 only the upper half of the formation was seen in open 

 section, as this is the only part ever quarried into, and 

 natural sections of Cincinnati strata are rare in this 

 region. But a few do exist in the southern and south- 

 western parts of Stephenson County, which show the 

 lower strata of the shales, and from an examination of 

 these, together with quarries and railway cuttings, the 

 following section has been prepared: 



Generalized section of the Cincinnati Group in Stephen- 

 son Co., Illinois. 

 Niagara Limestone. 



Light brown, argillaceous, thin-bedded limestone, 

 and white chert. Transition to Niagara, and counted 

 with it. 10 ft. 



1. Calcareo-argillaceous shales. Buff and gray, 

 with irregular patches of blue. Generally unfossil- 

 iferous. - - - - - 50 ft. 



2. Light brown, crystalline, dolomite layers, and 

 soft, yellowish shales. Fossils very abundant. - 15 ft. 



3. Coarse-grained, calcareo-argillaceous shales. 

 Light brown and red. Dark brown laminated shales 

 alternating with lower layers. No fossils. - 20 ft. 



4. Dark brown, argillaceous, finely laminated and 

 very fissile shales. No fossils. - - 5 ft. 



5. Same as above, except light brown in color. 3 ft. 



6. Stratum containing much reddish-brown pow- 

 dery iron oxide. - - - - 6 in. 



7. Yellow granular shale. - - - 8 in. 



8. Dark brown shales made up largely of com- 

 minuted shells. Fossils. - - - 4 ft. 



Galena Limestone. 



Since the remarkable discovery of oil and natural gas 

 in the Trenton limestone of Ohio and Indiana, and the 

 consequent discovery that the Utica shale of the New 

 York section is present in the two states mentioned as a 

 well-marked bed of dark brown shale, the writer has 

 thought it probable that the Utica shale, in its normal 

 condition, would be found to make up a part of the Cin- 

 cinnati strata of northwestern Illinois. 



Many of the "mounds" of western and southern Ste- 

 phenson County are capped with a few feet of Niagara 

 limestone, but the main body of the elevation is made up 

 of the light colored shales or shaly limestones aggregat- 

 ing fifty feet in thickness, and numbered one in the sec- 

 tion. This is certainly not Utica, but agrees pretty well 

 in stratigraphic and lithologic conditions with the Hud- 

 son River shales, as developed in southern Ohio. The 



evidence is still stronger for the Hudson River age of the 

 underlying fifteen feet of light colored shales containing 

 numerous limestone layers, literally covered with fossils, 

 which, so far as I know, are of typical Hudson River 

 species. 



The preceding strata are of a generally light color, but 

 in No. 3 dark colors begin to appear. It is probable that 

 wells drilled through the Cincinnati strata in this region 

 would be reported as passing through sixty-five feet of 

 light colored shales, then through twenty feet of grad- 

 ually darkening beds, and finally about fourteen feet of 

 dark brown shales. This agrees with well-section reports 

 from Ohio, differing, however, in the thickness of the 

 strata. 



No. 3 is so coarse-grained as to resemble sandstone, 

 but on dissolving the calcareous matter with acid the 

 grains are found to be composed principally of clay. 

 These gradually grow darker towards the base, and thin 

 strata similar to No. 4 appear, alternating with the red 

 sand-like shales. No. 4 is a very characteristic stratum 

 of non-granular, finely laminated dark brown shale, 

 weathering to a light blue color, and breaking into small 

 flat pieces, as does the Utica shale of the Atlantic slope. 



No. 5 is similar in constitution, but is somewhat lighter 

 in color, weathering to buff. The thin stratum contain- 

 ing the bright colored powdery iron oxide appears to be 

 made wj) largely of dark colored clay, but is not well ex- 

 posed. The underlying yellow shale is similar to parts 

 of No. 1, containing some irregular patches of blue, and 

 seems out of place among these dark colored shales. 



But now we come to the most remarkable of all — a four- 

 foot stratum of dark brown shale, made up largely of 

 fragments of small shells, irregular masses of iron disul- 

 phide, small rounded concretions of a slaty color, and dark 

 brown or black mud. Only one variety of shell remains 

 in an unfractured condition, and this is probably some 

 species of Singula. These dark shales lie on a series of 

 buff colored shaly limestones, also largely made up of com- 

 minuted shells, but which is undoubtedly the upper por- 

 tion of the Galena Limestone. 



The dark brown shales, Nos. 4 and 8 of the section and 

 included lighter colored strata, are apparently stratigraph- 

 ically and lithologically similar to the Utica shale as 

 developed in Ohio and Indiana, and although this terrane 

 in the latter state has been shown to thin rapidly towards 

 the west, it is considered quite probable that it does not 

 entirely disappear at least as far west as the region un- 

 der discussion, viz., StejDhenson County, Illinois. 



While the lower thirteen or fourteen feet of the so- 

 called Cincinnati shales of this region are considered to 

 be truly of Utica age, the succeeding twenty feet of 

 shales. No. 3 of the section, may be transition strata to the 

 Hudson River shales, which certainly have set in in char- 

 acteristic form by the time the base of No. 2 is reached. 



There is evidence tending to show that some of the 

 beds, especially Nos. 7 and S, thin out and totally disap- 

 pear in portions of the field, also that the dark brown 

 laminated shales, No. 4, thin out towards the west and 

 south, and perhaps the entire dark colored portion of the 

 series disappears before reaching the Mississipj)i River. 

 There seems to be an interesting field for future study in 

 this portion of the Mississippi Valley, and some curious 

 problems to solve. 



This preliminary note is published in the hope that 

 sections showing the lower portion of the Cincinnati 

 shales in other counties of this and neighboring states 

 will be reported for comparison in order to determine the 

 boundaries of each distinct formation, and the changes 

 which they undergo in passing from one region to another, 

 which is absolutely necessary for the proper understand- 

 ing of the early Silurian history of what is now northern 

 Illinois. 



