UPPER CRETACEOUS SERIES. 733 



doubtfully correlated with the lower horizons of the Eagle Ford shales and 

 the upper horizons of the Upper Cross Timber sand of the Brazos River sec- 

 tion. In lithologic characters too they very much resemble the Eagle Ford 

 shale and the upper bed of the Lower Cross Timber sand. There is a sudden 

 ascent from the massive limestone which underlies these shales up into the 

 shales, and at the point of contact the character of the rock changes entirely 

 and the fauna of the limestone disappears. 



Before taking up the division in detail, it will be well to speak of the man- 

 ner of the occurrence of the rocks of Eagle Mountain. 



Studies were made of the rocks on the north and east sides of the main 

 mountain, and for lack of time these were not worked as thoroughly as is 

 necessary for a complete report of them. 



A collection of tall peaks and rugged terrace-like mounts of porphyritic 

 and other trachytic rock, in all extending about four miles in every direction 

 from the center, forms Eagle Mountain. Eagle Peak, the tallest of the group, 

 rises some two thousand feet above the surrounding basin. 



Around the base,, on the north and east sides, there extends a fringe of 

 Carboniferous and Cretaceous rocks in a series of broken hills. 



The striking feature of the Cretaceous and even the Carboniferous rocks is 

 that they almost invariably dip towards the southwest, as is the case with the 

 rocks of Devil's Ridge, Flat Mesa, and Southern Quitman Mountain. In the 

 east side of Eagle Mountain, from the base nearly two miles inward, the Cre- 

 taceous limestones, sandstones, and shales, aggregating a thickness of three 

 thousand feet, dip regularly to the westward beneath the mountain, and the 

 porphyry has welled up and cut across the edges of the shale and sands or 

 has overflowed since the rocks have been tilted and eroded. In many places, 

 from the base to the top of the exposed stratified rocks, the porphyry of the 

 mountain has erupted as dykes across the strata, or passed up between the 

 tilted strata as intrusive sheets. 



The action of the igneous rock of Eagle Mountain upon the stratified rock 

 has made work on them complicated and difficult, by highly metamorphosing 

 them, destroying the fossil remains, and disturbing the strata. 



Three sections were made across the Cretaceous rocks of Eagle Mountain: 



a. Finney's Ranch section, at the south end of Eagle Mountain. 



b. Carpenter Spring section, near the middle of the mountain on the east 

 side; and 



c. Eagle Spring section, at the northeast end of Eagle Mountain. 

 Upper Cretaceous rocks were found only in the Carpenter Spring section. 



