210 J. Marcou — Jura and Neocomian of Arkansas, 



which has been called Paluxy sandstone near Comanche Peak 

 and at the Kent County section ; simply yellow and white 

 sandstone at the Pyramid Mount section ; and Cheyenne sand- 

 stone near Belvidere, Kansas. This third fades is the most 

 persistent, occupying all the western country from Kansas to 

 New Mexico, western Texas and very likely northern Mexico. 



B. Following the Trinity division and in concordance of 

 stratification we have the Tucumcari division, composed' of 

 blue marl at the base, containing a bed formed entirely of 

 Gryphcea dilatata var. Tucumcarii and Ostrea Marshii ; then 

 comes a yellowish limestone with two or three feet of white 

 limestone. The top of that formation has not yet been 

 described. Yery likely it exists at Monte Revuelto, in the 

 Tucumcari region. The Gryphcea Tucumcarii is found scat- 

 tered, more or less, through the whole division, but more 

 abundantly at the base. At the end of the deposition of this 

 formation, a great break occurred ; denudation on a large scale 

 swept away the greatest part of it, leaving now and then a 

 small remnant ; for instance at Belvidere, Kansas, where the 

 strata numbered 4, 5 and 6, by Mr. Hill seem to belong to the 

 lowest bed of the blue clay containing Grypluea Tucumcarii 

 of the Pyramid Mount section. At Kent, in Texas, the 

 superior part of the Tucumcari division exists with the 

 Gryphwa Tucumcarii; and more of that division will be 

 found in the region of the Pecos River valley and also on the 

 upper Canadian River region. As I have already said, the 

 strata of the Kiamishi Creek valley in the Choctaw Nation, 

 containing the original Gryphcea Pitcheri of Morton, may 

 belong to the lower part of the Tucumcari division. 



C. We next come to a new great period, the Cretaceous 

 age, beginning w^ith the strata containing an immense number 

 of Gryphcea Bmmeri. When I say that the Cretaceous begins 

 with the apposition of the G. Roemeri, it is only a means of 

 calling the attention of the observer in the field, for there are 

 some strata below the true zone of the Gryp>hcea Roemeri. 

 For instance at Comet Creek, Oklahoma, we have one bed con- 

 taining Caprotina Texana, with a form of Exogyra Texana ; 

 while at Black Hills, Kansas, we have thirteen feet of shales, 

 numbered 7, 8, 9 and 10 in the section of Mr. Hill, containing 

 no fossils, which very likely are already Cretaceous strata. I 

 recall that No. 6 of Mr. Hill's section belongs still to the Jura, 

 and that denudation or erosion very likely exists between num- 

 ber 6 and number 7, the last number beginning there the truly 

 Cretaceous series. The presence of " occasional minute peb- 

 bles " in No. 7, indicate the disturbance after the break 

 occurred at the end of the Jura, and is an important witness 

 of the denudation and erosion. 



