NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 27 



being somewhere near one-thousandth of a millimeter in diameter, and appearing 

 like the crystals in a fine-textured dolomite. In the granular matrix various curving 

 lines were noted, some of which were very thin embedded small bivalve shells. 

 Several thin sections, cut in three dimensions vertical to each other, of the rock 

 near Burk, consist largely of a tangle of irregularly bending and branching laminate 

 structures, about one-twentieth of a millimeter thick. These lie mostly fiat with 

 the bedding planes and enmesh a varying copious matrix, consisting in part of 

 structureless material, and in part of small lump-shaped bodies of lime. There are 

 also various shell fragments, and irregularly shaped impregnations of black bitumi- 

 nous material, scattered through the mass. The structure of the rock suggests that 

 it has been formed, at this point, to some extent from a multitude of thin shells 

 incrusted with lime, which became embedded in a calcareous precipitate mixed with 

 some fine clay. In the Beaver Creek basin and along Wichita River the rock is in 

 many places somewhat porous, and has a dark brown rusty color. These are evi- 

 dently secondary characteristics, due to solution and infiltration by the groundwater. 

 Irregular pockets filled with crystalline calcite must be ascribed to the same cause. 



GENERAL SECTION OF THE OUTCROPPING ROCKS. 



"Reviewing all the observations made on the outcropping rocks, it is to be 

 noted that less than one-half of all the localities described can with certainty be 

 referred to their proper position in a general section. The Beaverburk limestone 

 and the Bluff bone-bed are the only identifiable units in the field. Of these, the 

 Beaverburk limestone does not extend eastward beyond Iowa Park, and the Bluff 

 bone-bed is not known to extend farther than 4 miles east of Electra. Only in one 

 place were the field conditions such that a measurement could be made of the verti- 

 cal distance between these two key-rocks. This is near the Webb well, just west 

 of the west boundary of Wichita County, 4.5 miles south of Electra. At this place 

 a shallow well has recently been made, and a thin limestone, readily identified from 

 fragments as the Beaverburk Hmestone, has been penetrated at the depth of about 

 45 feet. In the low upland near this well, the Bluff bone-bed lies 20 feet above the 

 curb of the well, so that the distance between these two members in our section 

 is 65 feet at this place, as shown in section 30 [35 of this paper]. * * * 



"The beds above the Bluff bone-bed * * * consist of 30 feet of red clay over- 

 lain by some few feet of sandstone. This clay is also exposed north of the railroad 

 a half-mile east of Electra, and in the low bluffs around the artificial lake a mile 

 west of Electra, as well as in the breaks on the east side of Bluff Creek. 



"About midway between the two key-rocks there is at one place on Bluff 

 Creek a dark bluish-gray, or almost black, shale, only 2 feet thick, in which occur 

 some flat clay-iron concretions as large as a hand. These, as well as the shale 

 itself, contain fragments of leaves in which the vegetable structure is unusually 

 well preserved. 



"The sediments below the Beaverburk Hmestone are seen in several places 

 in a belt about 5 miles wide, following the north side of the Wichita, from Burk 

 Station southwestward. Such are the strata designated and described as i, 2, 3 

 in section 21; i, 2, 3 in section 26; i in section 27; and i, 2, in section 28. But in 

 none of these' places are there more than 30 feet exposed of the beds below the Hme- 

 stones. Section 25 [34 of this paper], which is in the north bluff of the Wichita 

 River, shows the thickest single exposure in the region, and exhibits 125 feet of 

 the sediments underlying the Beaverburk limestone. In all of these localities there 

 are a few feet of sandstone at from 25 to 30 feet below the Hmestone, and in the 

 deep section on the Wichita River just mentioned there are four such beds of 



