46
GENERAL DESCRIPTION.
CRETACEOUS.
After leaving the upper margin of the ponderosa marls at mile post 186, three and a half miles east of Terrell, rocks of the Cretaceous age do not occur anywhere along the line of the section. Indeed it may be said that, with the exception of a few salines of very small areal extent, such as Brooks and Steen salines, in Smith county, and a small saline in Anderson county, no actual exposures of any deposits of the Cretaceous age are as yet known to occur anywhere in that portion of the State east of the Trinity. These salines have already been described in the First and Second Annual Reports of the Survey, and need not be repeated here.
The Cretaceous rocks found at Grand Saline, in Van Zandt county, nowhere, so far as known, approach the surface, but are covered with over 180 feet of Tertiary sands, clays and shaly clays, and are only found in borings of the several wells put down for the purpose of obtaining salt. The upper series of the Cretaceous formation found in these wells appears to be a blue limestone mixed with streaks of sand and gray limestone, having a thickness of 42 feet in the Lone Star well, and 28 feet in the Richardson well, a few feet below which the salt deposit of 300 feet occurs.
While it may be possible that other Cretaceous islands occur in the area traversed by the section, the structural position of those known tends to the hypothesis that they do not, and that, during Cretaceous times, this region formed a triangular bay, of which the widest portion was towards the south. It will be observed from the locations of the islands already known, that the Texas areas have a course slightly west of south, or approximately parallel with the Cretaceous shore line several miles further west, those already laid down on the map of Louisiana, accompanying the Third Annual Report of the Geological Survey of Louisiana, show a course decidedly from northwest to southeast. These two lines, if prolonged, would converge somewhere near the southeast corner of the Indian Territory, or approximately within the area occupied by the Rocky Comfort Chalks of the Arkansas Survey.
Want of reliable data prevents any theorizing upon the connection between these Cretaceous areas, and numerous observations will yet be required to establish their relationship and true position with regard to the intervening bay-like area in which they do not appear.
"Third Annual Report, Geological Survey of Louisiana. F. V. Hopkins, State Geologist. 1872, p. 203.