On a Section of a Well at Kissingen
Authors: Sandberger F. 
Published: October 2009

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beds which have been pierced by the bore of the Schönborn Well (2001 feet 9 in. in depth) at the Upper Salinen, near Kissingen, have already been several times described, but, in the author's opinion, not in a manner which has led to a clear knowledge of them. He therefore examined carefully the specimens which still retained the original labels, and even conveyed them to Würzburg for analysis.

He considered it highly desirable, in the first place, to ascertain a datum-line remaining constant over a wide area; and such he determined to be the blackish-blue limestone which was bored through at the depth of from 1698 to 1740 feet (see Section, p. 6). It consists of two varieties—one pyritous and the other free from bisulphide of iron. The colour is deep blackish grey, the structure close, and the fracture almost conchoidal. A quantitative determination gave 60·20 per cent. of carbonate of lime, and 17·22 per cent. of carbonate of magnesia. The rock is therefore a very bituminous and argillaceous dolomite. It corresponds accurately with the upper-most bituminous Plattendolomit of the Zechstein of the Hartz and Thuringia, and with hand-specimens from Eisenach, Aschaffenberg, and Gera.

The upper boundary of the Zechstein-formation having been thus fixed, it follows that the strata overlying the above-mentioned Plattendolomit, and ranging from a depth of 1590 ft. 9 in. to 1698 ft. 10 in., belong to the lowest part of the Bunter Sandstone; while those that immediately underlie it, at a depth of from 1740 to 2001 feet, must be referred to the upper region of the Zechstein.

The limestones which were so repeatedly raised during the boring caused the reference of the former series to the Zechstein; but the author states, as the result of his examination, that they differ in all their relations from the deeper limestones occurring at 1698 feet and upwards, and, on the other hand, correspond in none of their characters with the Plattendolomit (the uppermost member of the Zechstein), and that they therefore belong to the Bunter Sandstone.

Limestones being particularly abundant in the lowest portion of the Bunter Sandstone in Thuringia and in the district of Magdeburg, and occurring even in two forms, viz. (1) as “Rogenstein,” often very coarse-grained, and (2) as close or fine-grained so-called “Hornkalk,” the author concludes, from the comparison of a very complete series of them, that the “Hornkalk” corresponds entirely in petrographical and chemical characters with the beds in question,—and also that beds of rock-salt, analogous to those of Stassfurt or Schönebeck*, cannot be reckoned upon in Franconia; for the strata in which they lie are but slightly developed on the southern margin of the Thüringer-Wald, and at the best contain very little saline matter.

Below the Plattendolomit of the Zechstein, from the depth of 1740 feet to 1884 feet follow saline clays of red, bluish, and brownish colour, which appear to be traversed by lines of anhydrite, or of white gypsum. Boiling water extracts from them a tolerably large quantity of alkaline chlorides (one specimen of the red saline clay yielded 3·21 per cent. of chloride of sodium with very little chloride of potash), and little of the sulphates; they are evidently the principal source of the saline contents of the Kissingen wells.

The still deeper anhydrite, from 1884 to 2001 feet, is dirty bluish-grey, very hard, and here and there contains druses, in which crystals of the mineral appear to have been formed.

At a depth of 2001 feet the boring was discontinued, in consequence of the breaking and jamming-in of the chisel; and the question therefore still remains, whether the anhydrite forms the base of the salt-bearing beds of the Zechstein in Yranconia, or whether it is only an intercalated bed between an upper very poor deposit, which owes its importance entirely to the mineral waters which derive their salt from it, and a lower and richer rock-salt formation.

That this is possible appears, e.g., from the fact that in the Triassic deposits of Baden and Lothringen the salt-bearing portion contains several divisions of the pure rock-salt beds, which are separated from one another by very thick beds of gypsum, particularly striking at Düheim in the Schwarzwald, near Dieuze, and at several other places in Lothringen.

It is difficult to believe that while there exists a thickness of 24 feet of pure rock-salt, associated with saturated brine, on the borders of the Franconian basin near Salzungen, at the neighbouring Neustadt well, which yields saturated brine, and at the Kissingen well further towards the centre, only poor saline clay should have been deposited. It is far more probable that a thick rock-salt deposit is hidden beneath the Anhydrite, and would probably soon have been reached by a continuation of the boring in the Schönborn shaft, and thus have shown the future of the Kissingen saline wells.

In conclusion the author epitomizes the results of his researches upon the section in the Schönborn-well in the accompanying section, and discusses the most probable mode of the formation of the Kissingen wells, the succession of the rocks, and their chemical condition.