416 LOW STAIN ON: 
between the Arctic and Pacific Oceans. The closing of these con- 
nections would modify the currents, change the climate, and permit 
immigration of faunal elements from other areas without any other 
geographic changes." 
Comanche jaunas.~—The whole of the Comanche series is here 
treated as Lower Cretaceous, because in the Texan area the top of 
the Comanche is the only natural and satisfactory major plane of 
division in the Cretaceous. Stratigraphic, lithologic, and paleonto- 
logic studies all lead to the same conclusion. Many European 
paleontologists believe that the upper or Washita portion of the 
Comanche is of Cenomanian age and hence referable to the Upper 
Cretaceous of European standards and the Mexican geologists, while 
adopting this view, advocate for their country a threefold division of 
the Cretaceous and call the upper part of the Comanche, including 
the Fredericksburg and Washita groups, Middle Cretaceous. These 
varying views as to the classification and correlation of the formations 
are not important in the present discussion of the succession and 
distribution of the faunas which are grouped under the term Comanche. 
These faunas show many facies varying from time to time and from 
place to place. There are littoral faunas, reef faunas, and deeper- 
water faunas, but the reef facies is perhaps the most striking and 
characteristic. And yet these different facies are all so intimately 
connected either by common species or by stratigraphic relations that 
it is appropriate to speak of the Comanche fauna as a whole. When 
the Comanche fauna is examined either as a whole or in detail it 
proves to be very similar to the Cretaceous fauna of the Mediterranean 
province in southern Europe, and it is strikingly contrasted with the 
Shasta fauna of the Pacific coast, although the Comanche area in 
Mexico closely approaches the present Pacific coast throughout that 
country. Ona previous occasion I have called attention to the charac- 
ter of the differences between the Shasta and Comanche faunas.* 
They are not made up of related forms differing specifically, but they 
consist mainly of different classes of animals so that they present 
t See Von Koenen Festschrift, p. 433, where J. P. Smith has suggested that periodic 
opening and closing of these connections are sufficient cause for the changes in Meso- 
zoic and later faunas of the Pacific coast. 
2 Jour. of Geol., Vol. V (1897), p. 608. 
