ENDLicH.] GEOLOGY SAN LUIS DISTEICT, SECTION B. 329 



ter case forming fertile areas ,are cut into them. The shales, of a dark-red 

 to a brown color, seem to increase considerably in thickness, and southeast 

 of station 79 compose the soil of a valley that is well cultivated. As 

 stated under the head of Carboniferous, a portion of this latter formation 

 is exposed at the western ascent of this vallej^, indicating- a more con- 

 siderable rise of the granitic country immediately west than is found any- 

 where along the old shore-line. White sandstones and single dolomitic 

 strata interchange with the red ones, while those beds referred to the 

 Jurassic formation seem to decrease in thickness. A careful study of 

 detail-stratigraphy and paleontological character of the formations of 

 this region would probably lead to very interesting facts bearing upon 

 age and arrangement of these beds referred to the Trias. South of 

 Saint Charles Eiver, no more Mesozoic beds were found, which can 

 probably be accounted for by the fact that the granite in its horizontal 

 exposure pinches out at that point, and, as far as could be seen, does 

 not appear again for considerable distance. From that point south- 

 ward, as far as section h extends, it was found that the Cretaceous 

 formation rests immediately upon the* granite. Cretaceous No. 1 

 is very distinctly defined throughout the southern portion of this 

 section, forming abrupt bluffs of a yellow to brownish sandstone, in 

 which a number of plants are found. In the vicinity of station 33 and 

 northward, its dip to the eastward is not very considerable, and remains 

 comparatively small for some distance north, at the same time conform- 

 able with the underlying Mesozoic strata. At this southern end of our 

 section the Cretaceous rest immediately upon the granite, and probably 

 a little farther south the Tertiary beds succeed it in this position ; while 

 north of the South Saint Charles Eiver, the Cretaceous is considerably 

 removed from the granite, having, at that point, but a very slight dip. 

 Undoubtedly erosion has had a very appreciable influence in this, by 

 carrying away large portions of the readily disintegrating sandstone. 

 Low bluff's characterize the formation north of Hardscrabble Creek, dip- 

 ping to the eastward at an angle of frequently 15° to 20°, retaining the 

 same character down to the Arkansas. At several intermediate points, it 

 seems to rest immediately upon the granite, as no red beds were noticed 

 between, and as seen at most places the yellow sandstone is succeeded by 

 a white one. Both time and the character of the country forbade our 

 spending many days in the plains east of the mountain-range, so that 

 the terminus of the Cretaceous area could not be accurately determined 

 there, but it seems to have only a limited extent, and that the Tertiary 

 beds set in very soon and continue. In the vicinity of Canyon City, the 

 Upper Cretaceous formations make their appearance, and the sandstones 

 are covered by a series of limestone and shale strata, both containing 

 fossils, and running out into the plains at a gentle dip. Low bluffs are 

 formed here, as a little farther north, by the limestones and sandstones, 

 while the softer shales, more readily yielding to atmospheric influences, 

 manifest their presence by forming shallow ravines and narrow valleys. 

 A little southwest of Canyon City, a warm spring of about 100° Fahren- 

 heit has its origin in the Lower Cretaceous limes and shales ; like all warm 

 springs, it is said to have a very beneficial influence upon persons affect- 

 ed by rheumatism, gout, &c. Besides this continuous stretch of Creta- 

 ceous, section b includes another portion connected with the Cretaceous 

 bay west of station 11. This is an arm of the bay of almost obloiig shape, 

 presenting a series of long, low bluff's, striking a little east of north. 

 As mentioned in the resume of section a, the dip of the strata composing 

 these bluff's is to the west, thus varying from that of the remaining Cre- 

 taceous. A narrow stratum of red sandstone, reclining on the eastern 



