116 Rev. A. Sedgwick on the Geological Relations and 



subdivisions of the formation. In crystals and large crystalline nodules, with red marl under the 

 yellow limestone, on the right bank of the Nid above Knaresborough ; very rarely, and in very 

 small crystals, in the marl beds in other parts of the series. 



9. Sulphate oj magnesia. — This salt effloresces in great abundance upon some earthy beds 

 of yellow limestone near the village of Bramham. It has been found by Professor Gumming and 

 Mr. Holme to contain a trace of muriate of magnesia*. Mr. Holme also found traces of muriate 

 of lime and muriate of magnesia in analysing specimens of magnesian limestone from Mansfield. 



10. Mui'iatc of soda Ax^medi (though in extremely minute quantities) through some of the 

 red beds near Mansfield f- 



11. Quartz, — This mineral in a crystalline form is very rare, notwithstanding the abundance 

 of siliceous matter which is mechanically mixed with the magnesian limestone. It is found lining 

 the cavities of some hard cherty beds in the escarpment west of Wallass. Siliceous nodules occur, 

 thouo^h very rarely, in some of the yellow limestone beds in the southern parts of Yorkshire. 



12. Mineral springs. — 1. Thorp Arch Spa rises in the lower part of the yellow limestone 

 on the right bank of the Wharfe. It is fetid, from sulphuretted hydrogen, and tastes of sulphate 

 of magnesia; but it has not, I believe, been analysed. 2. An extremely fetid mineral water 

 springs from the yellow limestone beds below the high-water-mark, near the southern extremity 

 of Hartlepool clilF. 3. Askerne Spa water rises through the upper thin-bedded limestone, but 

 it is secreted by the lower gypseous marls which are brought up behind the village by a fault J. 

 A fetid spring is said also to rise from the same beds near the village of Wadworth. 



Organic Remains. 

 Fossil Fish. 



An account has ah'eady been given of the discovery of the ichthyolites of 

 Midderidge and East Thickley§. Some of them appear to have been destroyed 

 before their value was understood. Others were fortunately preserved, but 

 dispersed into so many hands, that it was only through the kindness of several 

 gentlemen in the county of Durham (among whom 1 am bound particularly to 

 mention Lord Barrington, the Rev. T. Austin, the Rev. S. Gamlin, Messrs. 

 E. Pease and H. F. Smith of Darlington, and T. Randyll, Esq. of Stockton,) 

 that I became acquainted with the prevailing characters of these fossils. Some 

 other fine specimens (for an examination of which I am indebted to H. Blan- 

 shard, Esq. of London, and Henry Witham, Esq. of Edinburgh), have enabled 



* Fifty grains of the salt scraped from the Bramham limestone were examined by Professor 

 Gumming, and gave the following result : — Sulphate of magnesia, 47.40. Muriate of magnesia, 

 with a trace of iron, 0.13, An insoluble residue 2.45, was probably derived from the scrapings 

 of tlic magnesian limestone. 



t See p. 100, note. Since this paper was written, a trace of rock salt has been also discovered 

 in the formation near Pontefract, by Mr. Phillips. (Annals of Philosophy, December 1828.) 



+ For an analysis of this water, and an account of the structure of the neighbouring country, 

 see an Essay by Mr. Brewerton. Knaresborough Spa, which springs on the east side of the 

 Harrowgate road, is not added to the above list ; because it rises from ground which is covered 

 with diluvium, and is probably out of the limits of the lower sandstone. (See Plate IV. Sec. 2.) 



§ See Ghap, ii. § 2. p. 77. 



