The Columnar Basalt of Poult Sill. 99 



able structure than has ever been exhibited before. The hill 

 is situated near the high road from Walsall to Willenhall, and 

 about two miles from the former town. The basalt at this 

 place seems to have been originally protruded from the neigh- 

 bourhood of the Rowley Hills, about six miles distant, perhaps 

 shortly after the formation of the lower coal-measures, for in 

 an open working of the bottom-coal, to the south of the quarry, 

 the basalt is seen reposing on the coal itself, which has been 

 changed by contact into anthracite. In another section, 

 exposed by cutting a tramway from the quarry, coal shales 

 are seen to rest on the igneous rock, but they have not under- 

 gone any change ; hence it is tolerably certain that the protru- 

 sion of the basalt took place immediately after the formation 

 of the Bottom coal of the district. Mining operations have 

 recently been carried on completely under the knoll of basalt, 

 and no trace of any pipe or vent through which the stream of 

 molten matter could now has been discovered. Hence it is 

 now generally admitted that the stream must have had its 

 origin farther to the west, and after passing through the lower 

 coal-measures some distance, it found an opening, and thus 

 formed a large mound of igneous matter. The composition 

 and mineral characteristics of this basalt are the same as that 

 of the more remarkable localities in Scotland and Ireland. The 

 central part of the mound has been long worked away ; but, 

 from the general arrangement of the columns, and the way in 

 which they curve towards a point which would be directly over 

 the middle of the quarry, there is reason to believe that the 

 columns radiated regularly from the cooling surface of the 

 basalt, and in the interior of the boss, assumed a vertical posi- 

 tion. The workings on the north-eastern side show these 

 vertical columns for a space of about thirty yards, and many 

 of them are upwards of twenty feet in height. They are of 

 a rude pentagonal form, and in some cases above two feet in 

 diameter. Towards the top of the section the columns are 

 smaller, and bend over with great regularity. A few months 

 ago the Midland Geological and Scientific Society held one of 

 their usual field meetings at the quarry, and examined carefully 

 the geological features of the locality. The material is exten- 

 sively used for road-making and paving in the neighbourhood. 

 At the works of Messrs. Chance, glass makers, near Bir- 

 mingham, this basalt has been melted and cast into candle- 

 sticks, vases, and other articles, which take a tolerably high 

 polish, and somewhat resemble in appearance the black Derby- 

 shire marbles. The mass of basalt at the Rowley Hills has also 

 been extensively quarried for road purposes, and the largest 

 excavation shows a very rude columnar arrangement of tin- 

 igneous rock, but not nearly so well defined as that of Pouk 



