^^^' 55'] ^ ^^^^ ^^^ PATJLTED IIN'LIER IN TIDES WELL DALE. 239 



16. On a Sill and Faulted Inlier in Tideswell Dale (Derby- 

 shire). By H. H. Arnold-Bemrose, Esq., M.A., F.Gf.S. 

 (Read March 8th, 1899.) 



[Plates XIX & XX.] 



Contents. 



Page 



T. Introduction 239 



II. Description of the Area and its Geological Structure ... 241 



III. The Lavas and Intrusive Dolerite of the Inlier 242 



IV. Petrography 245 



(a) The Intrusive Dolerite or Sill. 

 (h) The Vesicular Lava above and below the Sill. 

 (c) The Columnar Clay. 



(cl) The Limestone below the Igneous Rocks. 

 (e) The Tuff near the Northern Fault. 

 {} ) The Lava-flows south of the Inlier. 



Y. Summary and Conclusions 249 



I. Introduction. 



The object of this paper is to describe an interesting series of 

 igneous rocks, about ^ mile south of Tideswell, and between that 

 village and the valley of the Wye (Geol. Surv. 1-inch map, 81 S.E.). 



The old marble-quarry in Tideswell Dale has been known to 

 geologists for many years, on account of the baked columnar clay- 

 underlying the toadstone, which was at one time well exposed. 

 N'umerous excursions have been made to the quarry, and several 

 papers have been written on it, but no detailed work appears to 

 have been done with the view of ascertaining the relation of the 

 toadstone to the clay and the limestone-beds. The quarry was 

 worked about 50 years ago for its fine coralline marble, but was 

 abandoned because of the unavoidable expense of removing a great 

 thickness of toadstone, in order to get at the limestone below it. 



In 1870 a paper was read before this Society by the Rev. J". M. 

 Mello, describing the section exposed in the quarry.^ In the same 

 year Mr. Edward Wilson^ and Mr. Edwin Brown ^ each contri- 

 buted a paper on the same subject to the Geological Magazine. 

 According to these observers, a bed of clay, which was often 

 columnar, rested on the coralline marble. It varied in thickness 

 from 5 to 12 feet, and the columns in it sometimes attained a length 

 of 8 or 9 feet, and a breadth of 6 inches. Above the clay was a 



- ' On an Altered Clay-bed & Section in Tideswell Dale,' Quart. Journ 

 Geol. Soe. vol. xxvi (1870) pp. 701-704. 



^ ' Altered Clay-bed & Sections in Tideswell Dale,' Geol. Mag. 1870 

 pp. 520-523. 



^ ' On a Columnar Clay-bed in Tideswell Dale, etc' ibid. pp. 585-586. 



