446 PROCEEDINGS OF THE ACADEMY OF [1890. 



less even surface has been prepared through aqueous erosion (and 

 sedimentation) and long-continued volcanic discharges, principally 

 the latter. Along the southern margin of the plateau the Creta- 

 ceous strata (emerging from the plateau) rise to an absolute eleva- 

 tion (above the sea) of upwards of 8,000 feet. 



5. The Cretaceous rocks, which form the nucleus of the plateau, 

 are projected (with little diminution in height) in more or les^ par- 

 allel ridges southward from the southern scarp of the plateau, 

 proving that the plateau uplift is not due to faulting on the east and 

 west line which marks the positions of the principal volcanic sum- 

 raits of tlie Republic. 



6. The Gulf plain of Mexico has been largely formed through 

 down-wash from the interior heights, but low-level limestones (with 

 little doubt of Cretaceous age) appear in places beneath the cap- 

 ping of volcanic sand and boulders. Marine Tertiary strata seem 

 to be restricted to the northern portion of the Gulf plain, and to 

 point off rapidly after leaving the Rio Grande. No marine Terti- 

 ary strata are known from the plateau region. 



7. The Cretaceous sea swept continuously across the Republic 

 from what is now the Gulf border to the Pacific, but strips or islands 

 of Azoic and Palaeozoic rock probably projected from this sea, much 

 as the peninsula of Lower California and the neighboring islands 

 to-day project from the Mexican Pacific. 



9. No true Lower Cretaceous beds exist (or have been so far iden- 

 tified) in either Texas or Arkansas, the Lower Cretaceous, so-called 

 (Comanche series, etc.), being not older than the Cenomanian (Mid- 

 dle or Upper Cretaceous). 



9. No marine deposits of unequivocally Lower Cretaceous age 

 have thus far been determined in the LTnited States east of the 

 Rocky Mountains. 



The earliest recognition of the existence of Cretaceous deposits in 

 Mexico is, I believe, contained in Galeotti's paper "Notice sur le 

 calcaire cretace des environs de Jalapa au Mexique," published in 

 the tenth volume of the Bulletin de la Societe Geologique de France 

 (pp. 31-39, 1839). Remarkably enough, this paper, although pre- 

 pared with much care and considerable detail, has been very gener- 

 ally overlooked by geologists, but in it the author strikes the key- 

 note to the geology of the greater part of the Republic. Galeotti's 

 researches cover various outcrops (" islets") of white, cream and 



