in the Hio Grande Y alley, New Mexico. 59 



North of Socorro County the Lower Carboniferous forma- 

 tions disappear by overlap, the rocks of the Pennsylvanian 

 series resting- directly upon those of pre-Cainbrian age. 



Lake Valley Limestone. — Above the Fercha shale (Devo- 

 nian) in western Sierra County is a series of limestones with 

 some shales, the upper beds of which at Lake Valley and Llills- 

 boro are filled with fossils. The Carboniferous age of these 

 beds was first recognized by E. D. Cope,* who, on the authority 

 of Dr. C. A. White, referred them to the Middle Carboniferous 

 (August, 18,81). 



S. A. Miller, to whom Cope submitted the fossils collected 

 by him at Lake Valley, publishedf a description of them, in 

 which he announces their Lower Carboniferous age and de- 

 scribes several species new to science. 



A little later (January, 1882), B. S. Silliman,^ on the author- 

 ity of Mr. Arnold Hague and Mr. C. D. Walcott, likewise as- 

 signed these beds to the Lower Carboniferous. This conclusion 

 was strengthened by the investigations of F. M. Endlich § in 

 1883, whose excellent section of the formations at Lake Yalley 

 is reproduced on page 61. In a paper published in 1884, F. M. 

 Springer || described the Lake Valley beds, and gives a list of 

 the fossils obtained from them. 



Ten years later Ellis Clark, at that time manager of the Lake 

 Valley mines, published a paper,!" illustrated by map and sec- 

 tions, in which the stratigraphy and ore deposits are described 

 with considerable detail. 



Following is a section of these beds obtained by the writer 

 at this locality : 



9. Capping of andesite. 



Lake Valley Limestone. (Mississippian.) 



8. Coarse, subcrystalline, yellowish-white limestone in moder- 

 ately thick beds, more shaly below. Abounds in crinoids 

 and other fossil forms. Some beds cberty. Full thick- 

 ness not shown 60' 



7. Blue shale including thin beds of bluish limestone contain- 

 ing the same fossils as No. 9, but crinoids not so 

 abundant 75' 



6. Grayish blue hard, compact limestone, more or less siliceous 

 at top. This is called the Blue limestone, and locally is 

 known as the "Footwall Lime" from the fact that it 



*Cope, E. D., Am. Naturalist, vol. xv, pp. 831-832, 1881. 

 f Miller, S. A., Journ. Am. Soe. Nat. Hist., vol. iv, pp. 306-315. 1881. 

 % Silliman, B. S., Trans. Am. Inst. Mng. Engrs., vol. x, pp. 424-444, 1882. 

 § Endlich, F. M., Am. Nat., vol. xvii, pp. 149-157, 1883. 

 || Springer. F. M., this Journal (3), vol. xxvi, pp. 97-103, 1884. 

 *f[ Clark, Ellis, Amer. Inst. Mng. Engrs., Trans., vol. xxiv, pp. 138-169, 

 1884. 



