118 G. W. Card—Flexihility of Rocks. 



In his great memoir on the Magnesian Limestone, Prof. Sedgwiclc 

 has the following passage : ^ — "The very thin laminje of the latter 

 {i.e. the earthy, finely-beddecl limestone) variety, which occur in 

 abundance near Marsden Rocks, are often slightly flexible, and very 

 fine specimens of flexible magnesian limestone with thicker laminoe- 

 occur in a bed near the middle of the cliff." The second reference 

 is that mentioned above, in " The Geology of England and Wales," 

 and is to the same effect ; while the third occurs in Bauerman's 

 Mineralogy- under the heading " Dolomite," where it is stated that 

 the stone is flexible when freshly quarried, implying that the 

 property is transient.^ 



It would thus seem as if the Marsden locality were the only 

 one from which flexible limestone has been described, but I was 

 fortunate enough to procure beautiful specimens on the coast a little 

 south of Sunderland, and therefore seveivil miles from Marsden, 

 which lies about two miles south of the mouth of the Tyne. For 

 some distance south of the Hendon dock the cliffs consist of Glacial 

 Drift ; passing this, and following the cliffs, now composed of 

 Magnesian Limestone, shortly before coming to the first point a 

 position is reached where considerable falls of stone occasionally 

 occur. It was from a recent fall that the specimens to be described 

 were procured ; the spot being about 1000 yards south of the Blue 

 House Inn. From a similar fall in Marsden Bay, on the south side 

 near the Rocks, I also obtained specimens, but these were inferior 

 to those from Sunderland, and will not be again referred to. 



The cliffs here are mainly composed of a laminated magnesian 

 limestone ; that from above being earthy, friable, and comparatively 

 unaltered, while in the lower portion of the cliff the stone, while 

 still tending to split along the bedding-planes, which are very 

 clearly marked, has been compacted by the re-crystallization of the 

 whole. It is from the upper part that the flexible variety comes. 

 Owing to the strike corresponding approximately with the trend of 

 the coast, the outcrop in the cliff is horizontal. Bedding is very 

 perfect, and many perfectly level slabs, of several square feet ia 

 area, have been brought down by the fall. It was from these slabs 

 that my specimens were procured ; and I see no reason why, with 

 care, very large specimens showing flexibility might not be obtained. 

 The colour of the stone is light yellow, the surfaces of the laminaa- 

 are coated with a yellow powder which soils the fingers, lamination, 

 is sometimes very perfect (-75 mm.), the whole being uniformly 

 very fine in grain, ami requiring careful handling because of its- 

 softness and friability. In general appearance it is, indeed, not 

 unlike a fine-grained sandstone, and appears to have resulted 

 chemically from deposition in successive layers.* 



An interesting feature is the occurrence of many minute nests of 



1 Trans. Geol. Soc. ser. ii. vol. iii. 1835, p. 87. 



* Text-book of Descriptive Mineralogy, H. Bauerman, p. 353. 



^ However it may be at Marsden, this is certainly not the case at Sunderland. 

 After having been kept in a dry place for several months, the specimens from thfr 

 latter locality have undergone no loss of flexibility whatever. 



* Sedgwick, op. cit. p. 86. 



