190 TRANS. OP THE ACAD. OF SCIENCE. 



The sandstones are very variable in character; they occur usually 

 in thick massive beds composed of fine, purely quartzose grains, loosely 

 cemented. Sometimes they appear in large even layers, from 1 to 12 

 inches thick, very hard or even flinty, and often finely ripple-marked ; 

 sometimes they split regularly into rhomboidal slabs, and sometimes form 

 irregular shells. 



la No. 6 I observed a thin seam of coal, extending with remarkable 

 continuity over many miles, so as to become a leading characteristic of 

 this subdivision. At one point I found the coal 6 inches thick ; but gene- 

 rally it is thinner, from 1 to 2 inches. Occasionally we find it represented 

 by a thin band of shale, with thin lamina; of coal here and there inter- 

 spersed through it. 



The Cypress Sandstone, No. 8, may be regarded as a more fully devel- 

 oped equivalent of the Ferruginous Sandstone of the Missouri Geological 

 Report, if the latter is not rattier a representative of several of these sand- 

 stones combined. To retain the name of Ferruginous Sandstone, which 

 may be well suited as a local designation in Missouri, for this rock in 

 Southern Illinois, would however be decidedly inappropriate. 



D — St. Louis Limestone. It attains a thickness of at least 200 feet, 

 perhaps much more, and is differently developed at distant points. The 

 Oolitic structure of some of the layers is a characteristic of the formation 

 in tnis district. Near Anna, in Union county, we find in the descending 

 order 



1. White and bluish, purely calcareous, and partly Oolitic Limestone. 



2. Siliceous gray limestones, usually of a close uncrystalline texture. 



3. The Jonesboro quarry rock, consisting of whitish semi-crystalline 



limestone, replete with remains of Bryozoa. 



4. Highly siliceous limestone, which has in places lost all its lime by lix- 



iviation, leaving merely a highly porous skeleton of chert — a thick- 

 ness, where fully developed, of 45 feet. As 1 have observed a similar 

 appearance, on a smaller scale, in the Jonesboro strata, I conclude, 

 in the absence of fossils in No. 4, that both must have been formed 

 under similar circumstances during the prevalence of the same gene- 

 ral conditions, and that, different as they may appear, they still be- 

 long to the same general formation. 



These minor subdivisions are, however, not preserved farther east, in 

 Johnson and adjoining counties. 



Underneath the St. Louis Limestone follow shales and siliceous slates 

 and some black laminated slate, equivalents of the black slate formation 

 of Illinois and Indiana, which is by good authorities considered as of the 

 age of the Chemung Group. To these shales and slates succeed well 

 marked Devonian strata. 



In conclusion, I wish to state distinctly, that Ihe frequent alternation of 

 sandstones and limestones of approximately the same thickness, which I 

 have described above, is not, as it might appear to the reader, the falla- 

 cious result of imperfect observation, and deceptively produced by faults 

 in the stratification ; but it is the true structure of the country, and can be 

 traced continuously over several counties. The dip of these formations 

 is nearly uniform a few degrees to the east of north, and, as many creeks 

 traverse the strike of the strata at nearly right angles, their succession 

 can be proved at numerous localities. Bold mcky cliffs are of frequent 

 occurrence in the district, and single ledges can sometimes be traced for 

 miles, rising in high points to the southward and then breaking off in pre- 

 cipitous bluffs. 



