192 Bulletin of Laboratories of Denison University [Voi. xi. 
The area immediately north of this sheet from the Zia res- 
ervation westward is very much broken by the erosion directed 
toward the Rio Salado. Deep defiles have been cut through 
the high escarpments looking toward the stream and much fault- 
ing has disturbed the uniformity of the exposures. Here it is 
possible to study the upper layers of the red series and the 
lower portion of the Cretaceous to good advantage in spite of 
the displacements referred to. 
The proximity of the gypsum and salt to great lignite beds 
is of great commercial importance for it will hasten the time 
when these resources can be made available. 
Resume of the Cretaceous.^ 
The American Cretaceous is essentially a transitional pe- 
riod; and, although its general paleontological features agree with 
those of Europe, its upper and lower limits cannot be as defin- 
itely defined. In Europe the Tertiary is nearly everywhere 
unconformable upon the Cretaceous, in America this lost inter- 
val is represented by the transition group known as the Laramie, 
while at the bottom of the series we have the transition group 
known as the Trinity. 
The American Cretaceous period is usually divided into 
the Upper and Lower Cretaceous, these, however, do not cor- 
respond to the Upper and Lower Cretaceous of Europe, but 
are based entirely upon conditions found in this country. It 
was at first thought that the Lower Cretaceous was wholly 
wanting in America and that a great gap existed here; but re- 
cently it has been found in several widely separated localities ; 
namely, in Texas (Comanche Grp.); in California (Shasta Grp.); 
in Canada (Kootanie Grp.); and on the Atlantic Border (Po- 
omac Grp.). 
The Cretaceous beds in England consist of 
Upper Cretaceous Chalk beds, 
with flint. 
^ The following notes were compiled for the present paper by Mr. H. O. 
Brooks. 
