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shells sometimes to such an extent as to be useful as a marl or fertilizer, as is seen on some hills near Col. Durant's, near Centreville, in Leon county. This rock is also in the hills of the petroleum region, near Melrose, in Nacogdoches, and is there by many, erroneously, supposed to belong exclusively to the oil-bearing rocks.

The rocks of the older tertiary are sedimentary deposits, including also the iron ores which often lie in beds or concretions in clays and sands. The deepest wells at their greatest depth generally have sands or friable sandrock, from which the water flows.

The following section is on the railroad cut east of and near Mineola, on the Texas Pacific railroad, in the northern part of Smith county:

This is not permanent; sometimes hard light clay and again a compact light jointed clay takes its place. Sometimes concretionary iron ores abound in these clays, which, however, are not strong clays, sand largely predominating.

The town well at Mineola, thirty feet deep, is through a mixed soil, varying from a yellowish light gray to a dark brown. Water abundant, but strongly mineralized with soda, copperas, alum and magnesia-hence little used.

There is a large spring of excellent water at the edge of the town, besides most of the other wells in the neighborhood out of town have good water, showing the formation in which the town well is sunk is not extensive.

Most of the wells south of this in the tertiary as far south as Robertson county, and including that county, also pass through sands and clay, or alternating with sandrocks and iron ores-the sands and clays generally so hard that the wells do not need curbing, the water being found at a depth of from fifteen to ninety or more feet, most wells being from twenty to thirty feet deep. Many of them pass through coal beds. Where the coal is not charged with sulphur, alum, etc., the water is good, as is exemplified in the wells at Head's Prairie, in Limestone county.