460 PUOUEEDINGS OF THE ACADEMY OF [1890. 



general lithological features of the formation — which is largely com- 

 posed of massive cream, gray and blue (partially bituminous) lime- 

 stones and marbles — and in the fossils which they contain. The 

 rocks over the greater part of their extent pitch at steep angles, but 

 in some districts they dip regularly and evenly over long distances; 

 in others they are badly folded and dislocated, and rapidly alter- 

 nate in inversions and fractures. This condition is especially well 

 marked on the eastern face of the plateau, and can be seen at many 

 points along the line of the Mexican Railway between the Boca del 

 Monte and Nogales. In the deep gorge of the Infierno, below Mal- 

 trata, the effects of crushing are exhibited on a wonderful scale. 

 The predominant strike of the formation seems to be N. W. — S. E., 

 with dips both to the eastward and to the westward, and it is carried 

 along this line, or in a direction more nearly north-and-south, in the 

 long declining ridges (as in the mountains of Tehuacan and Yaute- 

 pec) which continue the formation of the plateau into the lowland 

 beyond the southern scarp. In the first range of elevations facing 

 the Gulf, as I observed in the Chiquihuite Mountains near Atoyac, 

 the strike is directed N. E. — S. W. (with a steep dip to the south- 

 east), the limestone ridge trending off in the direction of the foot- 

 hills east of Jalapa ; possibly the special forces which built up the 

 giant trio of volcanoes situated on the eastern edge of the plateau — 

 Orizaba, the Sierra Negra and the Cofre de Perote — were the deter- 

 mining factors in producing this change in position. In the Atoyac 

 or Chiquihuite range the limestones are of a cream color, heavily 

 bedded, and compact in texture, much resembling in places litho- 

 graphic stone. 



For a long time I searched in vain for fossil remains in these rocks, 

 but eventually discovered, both above and below the town of Ato- 

 yac, a number of beds of limited extent which were densely charged 

 with organic fragments. Their condition of preservation was in 

 most cases too unsatisfactory to permit of either specific or generic 

 identification, but I determined the outlines of several Hippuritidse, 



Gryphea sp. indet., Nerinaa Castilli, N. hieroglyphica, Pterodonta sp. indet., and 

 among corals, Trochoseris sinuosa and Thamnastraa pediinctdata. From per- 

 sonal knowledge I can say but little regarding these determinations. The identi- 

 fication of the HippuritidiB and the Nerinceas is probably in the main correct. I 

 have myself observed the foimer in the rock of Coalcoman, and Barcena mentions 

 Radiolites MendozcB {=^R. foliaceus ?), in association with Hippurites and Neri- 

 naa Castilli, as occuring in the State (Anales del Museo Nacional, 1877). The 

 determinations of the species of coral are, with little doubt, erroneous. 



