1890.] NATURAL SCIENCES OF PHILADErj'HIA. 4G7 



variation in tlie direction was possibly due to intnision-\var])ing. 

 For some distance around the volcano, however, the limestone beds 

 were shattered into cubical blocks; how far this condition may 

 have been induced through volcanic pressure, I cannot say, but it 

 seems probable that the breakage is not a simple form of jointing. 

 Some of the loose blocks of limestone show distinct traces of scorch- 

 ing and semi-fusion, and are manifestly products of eruption ; they 

 are in part crystalline, breaking along well-defined cleavage planes. 



We found numerous fossils both in the ejected boulders and, m 

 situ, in the stratified layers; unfortunately, their condition of pre- 

 servation was such as not to permit of specific recognition in most 

 cases, but there was no difficulty in determining the outlines of 

 various Hippuritidse, and of seemingly the same forms which we had 

 already observed in the limestones and marbles of Orizaba. The 

 same fossiliferous limestone outcrops at various placfcs in the town 

 of Yautepec and forms the Cerro de Calvariajust outside (east) of 

 it. Beautiful exposures are seen along the small stream which, in 

 the center of the town, forms the parting between the limestones and 

 the lava stream which enters from the west ; a strong easterly dip is 

 here well shown. There is no doubt in my mind that the limestones 

 of this region, with a pronounced easterly dip, are part of the same 

 series which, further to the east, in the region about Tehuacan, dip 

 in the opposite direction. They represent one section of a chain of 

 folds which passes continuously from the eastern face of the plateau 

 far into its interior, or even completely through it, likewise travers- 

 ing it from north to south. How many inversions or compressions 

 are involved in this gigantic mountain uplift, research has not yet 

 made clear. 



From the summit of the Calvaria hill the eye can readily trace 

 the backbones of the various ridges as they trend southward, until 

 they are lost from view. At their further end these ridges probably 

 inosculate with the series of heights whose trend is directed more or 

 less nearly at right angles to them, and whose age belongs to a much 

 more ancient period of geological time. 



Paleontology. 



With few exceptions, all the fossils that have heretofore been de- 

 scribed from the Cretaceous deposits of Mexico are enumerated in 

 the preceding pages. I append herewith a list of a few of the species, 

 "with their recognized distribution, which will serve more clearly to 



