1890.] NATURAL. SCIENCES OF I'HILADELl'HIA. 461 



as well as of their finely striated cortical surfaces. The latter in 

 section much resemble some of the giant Foraniinifera, while the 

 cups, where they partially protrude from the rock, strikingly recall 

 the rugose corals. I have little doubt that it is from these resem- 

 blances that some of the Mexican (Cretaceous) limestones have from 

 time to time been referred to the Paleozoic period, and it was some- 

 time before I could myself determine the precise nature of the fossils 

 which it was my good fortune to discover. No mention of their 

 occurrence in these rocks is, so far as I am aware, made by any ear- 

 lier investigator. The discovery is particularly interesting since it 

 helps to delimit the eastern boundary of the Cretaceous deposits at a 

 point far removed from the actual crest of the plateau. To what 

 extent these same rocks extend Gulf-ward beneath the capping of 

 lava, boulders and volcanic sand which fills in the basal plain east 

 of the first true range of mountains, I could not ascertain. But it 

 is certain that the limestone is largely developed in these eastern 

 lowlands, and it is more than probable that the outcrops which 

 appear in and about the line of the Vera Cruz-Jalapa railroad, such 

 as I had occasion to observe at Plan del Rio, at an elevation of 

 about 1000 feet above the sea, are a continuation of the Atoyac 

 rock, just as the fossiliferous rocks about Jalapa and Coatepec are a 

 continuation of the rocks of Orizaba. I failed, however, to find any 

 trace of fossils in the rock of Plan del Rio, nor could I obtain any 

 positive information from the natives that any such fossils had been 

 found ; but the rock is lithologically very similar to that of Atoyac, 

 which is also largely non-fossiliferous, and it lies directly in the line 

 of strike of the Chiquihuite mountains — i. e. in a line parallel with 

 the eastern crest of this portion of the plateau. 



The Cordoba Mountains, which succeed the Chiquihuite range 

 westward, are without doubt a part of the same system of elevations 

 which begin with the latter as their lowest crest and culminate in 

 the chain, rising to a total elevation of some 8500 feet, which passes 

 southward from the plateau in the region of Esperanza. Being pro- 

 jections on the plateau itself, this chain presents the appearance of 

 insignificant hills, but the crests can be followed fifty or more miles 

 southward, along the declining valley of the Rio Salado, when the 

 full height of the mountains appears in thousands of feet of elevation. 



The typical fossiliferous strata of the Upper Cretaceous period are 

 beautifully exhibited in the steep beds of the Cerro de Escamela, 

 just outside of the town of Orizaba. Fossils are here very abund- 



