84. 



I cannot take leave of the pala?Ozoic rocks of our own 

 islands without communicating to the Society a fact, wliich^ minute 

 as it may seem to be, is of interest in ]"egulating our views re- 

 specting the development of animal life. The Rev. P. B. Brodie, to 

 Avhose researches in the secondary rocks I shall presently allude, 

 informs me, that he lately discovered in the Silurian limestone on 

 the west flank of ?'Jay Hill, Gloucestershire, two palates of fishes. 

 Now as the rock in question is of the age of the Wenlock lime- 

 stone, we learn that fishes existed in the inferior "as well as in 

 the superior member of the Upper Silurian rocks, in which they 

 had previously been noticed. No trace, however, of Vertebrata has 

 yet been discovered in the widely extended and enormously thick 

 Lower Silurian deposits. 



Igneous Rocks of South Staffordshire. — As connected with the 

 older depositary rocks of the central counties of England, I will now 

 direct your attention to some recent observations on the changes to 

 which they have been subjected by igneous agency. Besides form- 

 ing a most instructive museum, singularly rich in Silurian and Car- 

 boniferous species (including many unpublished), the Geological 

 Society of Dudley, to the establishment of which I last year alluded, 

 has produced a report ' On the Igneous Rocks of the South Staf- 

 fordshire Coal-field*,' not yet printed, with the results of which I 

 am convinced you will thank me for making you acquainted. In 

 the southern portion of this coal-field there are centres of eruption 

 where the basaltic and trappean matter, rising from the bowels of 

 the earth, completely cuts through the surrounding carboniferous 

 strata, dislocating and altering them in the manner which has been 

 pointed out by Mr. Keir, Mr. Arthur Aikin, and other observers, 

 including myself. In regard to the lateral injections of the igneous 

 matter among the coal strata, Mr. Blackwell; by comparing the 

 shaft-sections of contiguous collieries, has shown, that however a 

 single vertical section might seem to afford grounds for belief, that 

 such igneous matter had been formed as a bed, yet that in reality it 

 traverses various depositary strata in a slightly oblique direction, 

 and often thins out in the form of a wedge. From such apparently 

 horizontal masses, vertical dykes, with occasional lateral veins of 

 white felspathic rock, varying in thickness from a few inches to 

 three or four yards, are seen to rise up and traverse the coal-beds 

 in the most irregular manner, though such dykes are not found to 

 produce any derangement in the regular measures. Another good 

 fact observed in relation to a supposed horizontal sheet of basalt in 

 the midst of the sedimentary strata, is, that the beds on which it 

 rests are less subject to faults and dislocations than those which lie 

 above it ; the intruded mass, indeed, sometimes rising up to the 

 surface and forming a knoll, occasionally bare, and at other places 

 covered by the coal strata, which mantle round it. 



The report also proves, that some of the chief faults which radiate 



* The Report to which allusion is here made, including the Sections, was 

 drawn up by Mr. J. H. Blackwell of Dudley, assisted by Mr. W. Spencer. 



