152 CHARLES R. KEYES 



Ladronesian is a title applied to the only coal-bearing forma- 

 tion of the entire section under consideration. This series now 

 exists only in remnants of a formation that was once evidently quite 

 extensive. It consists chiefly of shales and sandstones with thin 

 coal-seams. The formation rests unconformably upon the rocks 

 beneath. Profound Carboniferous erosion has all but completely 

 obliterated all evidences of its existence. The shales carry inter- 

 esting coal plants, chiefly of lepidodendrid types. There is but 

 small doubt that the formation is the representative of the Arkansan 

 series of the Ozark region. 



Resting unconformably upon all rocks beneath is the great blue 

 and gray limestone plate which is that portion of the Carboniferous 

 section with which most travelers have come into contact, and 

 which is most familiar. Farther west the lower portions have been 

 called the Aubrey limestones. To the south the major portion 

 is known as the Hueco limestone. The upper part of this unbroken 

 limestone sequence is absent over all of Arizona and New Mexico, 

 except in the extreme southern part of the latter. Faunally, as 

 well as stratigraphically and lithologically, the great plate is sep- 

 arable into three distinct sections. These three formations, which 

 have serial rank, are the Manzanan, the Maderan, and the Guada- 

 loupan series. 



The Manzanan series is composed chiefly of massive blue and 

 gray limestones with some thin gray shale layers. The fossils are 

 essentially those which characterize the Missourian series of eastern 

 Kansas. In the northern half of New Mexico this formation 

 reclines directly upon the eroded surface of the Acrhoezoic and 

 Proterozoic crystallines. 



Above the Manzanan series, and apparently continuous with 

 it, is a lithologically similar formation, though it is more of a gray 

 color, and often having dark layers intercalated. It is termed 

 the Maderan series; and it carries the so-called Lower Permian 

 fauna of Kansas. It is paralleled approximately with the Okla- 

 homan part of that succession. This hard limestone formation 

 is the rock-floor over a considerable portion of northern Arizona 

 and west-central New Mexican region. It is this formation that 

 manifestly constitutes the chief part of the Hueco formation of 

 Trans-Pecos Texas. 



