DATES OF ERUPTIONS. 



77 



for elementary study, as it requires long practice to decipher correctly such dark pages 

 in the history of the earth. 



To the phenomena, however, illustrating the stratified trap rocks of the Silurian 

 System, the reader will not be invited for some time, as he must previously accompany 

 me in descending order through many overlying deposits, till we reach the older Silurian 

 rocks, occupying the western part of Shropshire and adjacent parts of Montgomery- 

 shire, as well as large portions of Radnorshire ; districts which, (as far as my knowledge 

 goes) are unrivalled in the British Isles, for the number and clearness of the illustrations 

 bearing on this interesting point of inquiry. Let not my reader imagine, it is here 

 asserted, that contemporaneous and bedded trap rocks, similar in kind to those of the 

 Silurian System, do not sometimes exist in overlying formations ; reasons, indeed, will 

 hereafter be adduced which favour the belief, that even in a part of the region under 

 consideration, rocks of this character have been elaborated during the carboniferous sera, 

 though not in the same striking manner as in the Lower Silurian epoch. The " trap 

 tufs" of Hales Owen, hereafter to be described, must either belong to this class, 

 or be Considered as regenerated deposits, the trappean ingredients having been derived 

 from preexisting and solidified masses of rock. This ambiguous point will be fully con- 

 sidered in the chapter on the Dudley coal-field. But in other parts of the kingdom the 

 secondary formations afford proofs of these phenomena. Thus, in Devonshire, Mr. De 

 la Beche has recently observed the existence of trap, which from its relations, he con- 

 ceives must have been ejected during the formation of the lower members of the New 

 Red Sandstone of that district 1 . Again, in the North of England, Mr. Hutton has at- 

 tempted to show, that the eruption of a large portion of the whin-sill or basalt of Nor- 

 thumberland and Durham was coeval with the carboniferous epoch, whilst another 

 portion of it has been demonstrated by Professor Sedgwick to be of comparatively 

 recent date 2 . Such examples are quite in accordance with natural laws ; and as our 

 field of observation extends, there can be little doubt, that the phenomena of bedded 

 and contemporaneous trap rocks will hereafter be recognised in many deposits of 

 different ages. 



As this work professes to describe geological phenomena in descending order, or in 

 other words from the more recent to the more ancient, it might be expected that this 

 general view of their origin, would be immediately followed by a description of the trap 



1 Geol. Proc, Phil. Mag., vol. vii. N.S. p. 513. 



2 Hutton on the stratiform basalt associated with the carboniferous formation of the North of England, Trans, 

 Nat. Hist. Soc. of Northumberland, &c, vol. ii. p. 187. 



Having examined a part only of the country described by Mr. Hutton, I cannot pretend to oppose my opinion 

 to that of one who has so ably explored the whole of it ; but as far as I saw them, the phenomena in the valley 

 of the Tees (High Force, &c.) appeared to me to support the views which Professor Sedgwick had previously 

 drawn from an examination of that portion of the tract in question. On this point, however, Professor Phillips 

 justly observes, " It is not necessary to suppose that only one submarine flow of basalt occurred, any more than 

 to confine it to one opening." Geology of Yorkshire, vol. ii. p. 85. 



K 



