\ 



On the Hoiighite of Prof. Skepard. 361 



A most important economical feature of these rocks is the 

 presence^ especially westward, of iron ore which sometimes 

 passes down into the member below. The soil everywhere con- 

 tains sufficient oxyd of iron to color it deeply. 



This member is mostly the surface-rock of the table-lands sur- 

 rounding the basin, and usually appears a few miles in the rear 

 of the escarpments, increasing in thickness as we approach the 

 mountains on the east, or the hilly ridges of Southern Kentucky 

 on the north and northwest. (^ 6.) 



From my own observations, and the best data I can collect, I 

 infer the member to be from 250 to 300 feet thick, making the 

 entire group 450 or 500 feet- 

 Owing to the present imperfect state of our knowledge of 

 American carboniferous species, it is impossible to give a satis- 

 factory list. The following is presented, 



1. Syriiigopora reticulata, Gold? 



2. Lithostrotion, sp.? 



3. Cyathopliyllum, spj __. „^. ,. 



4. Fenestella retiformis, Schlot. ? and' II Or this, ' « 



other species. j 13. Terebratula serpentina, A Koa 



0. Syubuthocrhms Tennesseae, Troost I j 14. Pleurotoiuaria, sp. ? 

 6. Agaricocrinns tuberosus, « I ^ 



V. Conocrinus tuberculosus, " ! 



8- Granutocrinus cidariformis. 



9. PlatvcriniiB Saffordi, Troost. 



10. Productuscora, A.d'Orb.andothersps. 



11. Spirifer, several sp's. 



15. Euomphulus, three sp's. 



16. Boiler uphou, sp. ? 



1 7. Acephala, several genera. 



Art. XXXYII.— On the Hoiighite of Prof Skepard; by 



S. W. JoHNsoNj of the Yale Analytical Laboratory. 



Read before the Am. Assoc, for the Advancement of Science, at Albany, Aug. 1851. 



On page 314 of the Proceedings of the meetuig of this Asso- 

 ciation held at New Haven last year, occurs a notice of the min- 

 eral Houghite by Prof. Shepard. More than two years since I 

 noticed specimens of this mineral from Dr. Houghj and then pur- 

 posed to examine it- The specimens which were in my posses- 

 sion at the time of the publication of Prof. Shepard 's paper, and 

 "V^hich furnished the material for my analyses, agree in the main 

 '^^ith his description ; and it appeared improbable that any chemi- 

 cal species could be made from them as they were exceedingly 

 variable in composition as well as in appearance. It commonly 

 occurs as small imbedded nodules, usually more or less flattened, 

 with the interior dark gray or bluish gray and the exterior white. 

 Experiment and observation unite in proving that the differ- 

 ence in color between the external and internal portions of these 

 "concretions" is due to difference of composition. The milk- 

 w^iite parts contain carbonic add, the bluish-white portions do 

 ^^t. Further, some specimens are milk-white throughout, while 

 ^hers are almost entirely of a bluish tinge, and semitransparent. 

 The specimens at mv command for analysis were uniform in ap- 



