24 GEOLOGICAL MEMOIRS. 



that they belong to an older order of things than the tertiary. The 

 different divisions of the Jura-formation, the Keuper, and theMuschel- 

 kalk in this neighbourhood are greatly broken up and dislocated. 

 Wherever the upper division of the Jura, which in this quarter is 

 the Coralline Limestone, shows itself, the pea-ore in greater or lesser 

 beds is sure to be found, the Coralline Limestone always forming its 

 base : while the Tertiary formations spread themselves indifferently 

 over all the divisions of the Jurassic, Keuper, and Muschelkalk for- 

 mations. It is clear from this that the pea-ore is connected with 

 the Jura-formation, which has been broken up and dislocated after 

 the deposition of the pea-ore and previously to the deposition of the 

 tertiaries. The few fossils which are found in the pea-ore beds, 

 and even in the ironstone itself, as well as in thehornstone and jasper- 

 concretions, all belong to the Coralline Limestone, e. g. Cidaris Blu- 

 menbachii, Goldf., Astrcea, Foraminifera, &c. If it is asserted that 

 these animals did not live at the period of the deposition of the pea- 

 ore, but that they existed previously, and that their remains were by 

 some metamorphic process changed into iron-ore, &c. (which is very 

 possible), still it is certain that these fossils, when in their original 

 habitat, are never accompanied by any of a later date. 



The surface of the Coralline Limestone, where it forms the imme- 

 diate substratum of the pea-ore, is worn down and eaten into by re- 

 markable winding cavities. It is usually accompanied by variegated 

 clays and pure quartz-sand, materials not found in the Jurassic for- 

 mation, and which must either have been introduced together with 

 the pea-ore, or been formed out of the previously existing rock by 

 those chemical influences from which the pea-ore resulted. The Co- 

 ralline Limestone itself, where in immediate contact with the pea-ore, 

 has peculiar properties, as for instance, a very distinct vitreous frac- 

 ture. A remarkable instance of this kind is seen at Roppe, near 

 Befort, where an extensive bed of pea-ore is worked partly below 

 ground and partly at the surface in a cavity of a limestone which 

 probably is the Coralline. The limestone is furrowed on its surface 

 with long grooves, at the end of each of which lies a concretion of 

 pea-ore, which fills up and closes the groove. These appearances are 

 all satisfactorily explained by the theory long ago put forth, and now 

 perfected by M. Gressly, which refers the origin of the beds of pea- 

 ore to the chemical effects of hot springs, containing iron and other 

 substances in solution, poured out upon the limestone probably about 

 the close of the Jurassic period. Dr. C. Burckhardt, who looks upon 

 this explanation as the most natural, remarks that, from Burg and 

 Klein-Liitzel to Laufen, the pea-ore is found accompanied by fossils 

 of the so-called Sequanian system, a subdivision of the Jurassic 

 system, which immediately reposes on the Coralline Limestone. 



[J. C. M.] 



