RESUME OF LITERATURE. 89 



The Paleozoics south of the Arkansas (sections 5 and o of Endlich's district) come 

 in the area which I have defined for my purposes and named the Sangre de Cristo 

 region. Here the Silurian is again found, though in small quantities, but the 

 Carboniferous occupies larger areas. The latter consists chiefly of the Arkansas 

 sandstone, which forms the main bulk of the Sangre de Cristo Eange. The typical 

 Arkansas sandstone is here found to be more or less interstratified with dark shales and 

 isolated limestones, the combined thickness of which is said in one instance probably 

 to exceed a mile. The lower limestone, determined by its petrographic character 

 and position, also occurs south of the river, and accompanies the Arkansas sandstone 

 for some miles. No fossils were found in it (pages 326,327). 



Farther west, along the southern end of the Arkansas Valley (in section c of 

 Endlich's district), the Silurian is again reported. It consists of light-colored 

 quartzites of j'ellowish, bluish, and reddish tints, which are conformablj^ overlain 

 by gray to bluish limestone with siliceous segregations. Lithologically they are 

 said to be identical with those found north of the Arkansas River. 



One can hardly doubt that in this instance the quartzite is the Sawatch quartzite, 

 and that the limestone is the equivalent of a similar bed at Fossil Ridge, in the Elk 

 Mountain region, of the basal limestone at station 53 in the South Park region, and 

 of the Yule limestone of established sections. Endlich calls attention to the resem- 

 blance which these strata bear to those north of the river, ?jut in the latter area 

 the quartzite is represented as lying upon instead of under the limestone, so that its 

 position is not that of the Sawatch but of the Parting quartzite. The Sawatch, 

 indeed, appears to be wanting, but I can not altogether banish the suspicion that the 

 sequence is wrong in Endlich's sections north of the Arkansas. 



In the Haj'den report for 1875 " is found Endlich's account of the geology of the 

 so-called Southeastern district. He described the boundaries of this district in the 

 following terms (page 105) : ' ' The district assigned to our party during the field season 

 for 1875 extended from longitude lOiP 30' west to longitude 108° west, was bordered 

 on the south \)\ north latitude 36° 45' and on the north bj^ north latitude 37° 50'. On 

 the west side it connected with the work of 1871, and on the north with that of 1873." 

 The geologic discussion is distributed into five divisions based upon geographic 

 occurrence. These are the Sangre de Cristo Range and the Huerfano region, the 

 San Luis Valley, the southern extension of the Sawatch Range, the Rio San Juan and 

 its drainage, and the Post-Cretaceous formations of the Trinidad region. Only one 

 of these chapters, that upon the Sangre de Cristo Range, contains anything of 

 importance in our discussion. 



Though present in the more northern portion of the Sangre de Cristo Range (see 

 Endlich's report for 1873), the strata of Silurian and Mississippian age gradually 



(lU. 3. Geol. Goog. Slirv. Terr., Nimh Ann. Kept., for 187.5, 1877, pp. 103-215, 



