Dr. Henry Woodioard — 'Photography in Geology. 411 



(p. 12.) '■'■No. 1664. Bedding and Jointing in Carhoniferous Sandstone ; JfTuch-o^ 



Head, Donegal. 

 . ■., , ' ■■ ■ Pliotogmphed by K. Welch ; 1890. ' , , ; ', 



At Mucki-Qs Head, in the west of Co. Donegal, au outlier of LoAver Carboniferous 

 'sandstone and limestone rim's out into the sea.' , The horizontal bedding and rertici^l 

 ■joints control the weathering of the cliff, and ledges of more resisting 'reck pro ject 

 boldly from the wall.- The two vertical series of joints are fairly perpendicular to 

 each other. In certain beds lamination is well exhibited. , . '; 



' GiiENViLLE A. J. Cole." 



Gf the pliotographs dealing with volcanic subjects maybe specially 

 mentioned a fine example of a basalt dyke taken by Mr. R. Welch^ 

 (B.A.) 974, and described by Mr. W. B. Wright. The dyke is seen 

 cutting through the chalk on the south side of Cave Hill, Belfast, 

 CO. Antrim. The chalk itself is converted into a hard white lime- 

 stone, in which may be seen wellrdefined layers of flint. A flow of 

 lava rests upon the eroded surface of the chalk, the latter being 

 covered with a bed of flint gravel, most of the flints in which are 

 stained a deep red colour. 



Another fine photograph, also taken, by Mr. R. Welch, is (B.A.) 

 1652) and represents a portion of the columnar basalt of the 

 Giant's Causeway,. CO. Aiitrim, described by Professor T, G. 

 Bonney, F.R.S. ':..■,.• 



(p. 18.) "iVo. 1652. Columnar Bascdt, Giant'' s Cau'seivay, Antrim. 



Photographed by R. Welch ;■ 1893. 



Columnar jointing, is rather common- in' basalt, and that of the Giant's. Cause way 



affords excellent examples. As the structure; is due to . contraction in. cooling; the 



columns are usually six-sided. (S. Mallet, Phil. Mag., ser. iv, vol., i, p. 122). Furthet 



contraction produces cross joints. These may be'fr'equent, as in. this, instance, or at 



■ rather, long intervals, as in the Siebengebirge. Their form varies ; it is sonietimes 

 a plane ; sometimes part of the surface of a large sphere, covering all the end except, 

 perhaps, the angles,' as with most of those in this photograph : sometimes an almost 

 hemispherical dome rises in the middle of a flat roof. The curves, as can be seen, do 



' not all point in the same du-ection. Occasionally spheroids, which maybe concentric,, 

 form inside a colunm without external rupture, and are only exposed by weathering. 

 A column in the bottom left hand corner shows a tendency to this sti'ucture, which 

 also may be exhibited in the occasional fractures at the corners of the. blocks. This 

 is a result of the principle of least-action, but difficulties often arise in applying that 

 to-particular instances (Quart. Journ. Geol. Soc, xxxii, 1876, p. 140). ■ 



T. G. Bonney." 



There is another volcanic picture, that of the well-known 

 " Scuir of Eigg" (No. 2562), photographed by Mr. Arthur S. Eeid, 

 M.A., F.G.B., who also gives a detailed description of the same, and 

 refers the reader to Sir A. Geikie's great work on the Ancient 

 Volcanoes of Great Britain, 1897, vol. ii, pp. 236-248. 



A fine example of erosion is seen in the photograph taken by 

 Mr. E. A. Bush, of the Hemlock Stone, Stapleford Hill, Notts, 

 described (p. 10, No. 2879) by Mr. Walcot Gibson, F.G.S. This 

 stone is a column 31 feet in height and 70 feet in girth, and is ah 

 ex:cellent illustration of erosion by wind action and atmospheric 

 weathering. 



Professor E. J, Garwood contributes a beautiful photograph 

 (No. 624) and description (p. 17) of the intrusive igneous sheet in 

 Carboniferous rocks known as the Whin Sill; High Force, Teesdale. 

 This is a classical waterfall described by Sedgwick in 1823. The 



