TRAP ROCKS OF TORTWORTH. 



457 



so small, indeed, that it is only by occasional cuts and improvements in the roads that 

 they can be detected 1 . 



Of the fossils of this formation, the Pentamerus lesvis is perhaps most abundant, but 

 others are scarcely less frequent, such as the ornamented small Trilobite (Trinucleus 

 Caractaci), the Tentaculites of Schlotheim, as well as those corals which have been cited 

 as so abundant at May Hill, and in Shropshire. The round impressions of encrinital 

 joints scattered over the faces of the stone constitute one of the best empirical tests of 

 this sandstone. The application of this proof, however, must be made with care, for 

 there are rare examples of such impressions in the Ludlow and superior rocks. Their 

 profusion, however, in the Lower Silurian rocks is very striking. 



On reference to the description of the organic remains it will be seen that many 

 have been figured from this district ; but it is not pretended that the list comprehends 

 all the fossils of this interesting tract ; for as soon as a sufficiency of specimens were 

 acquired for the identification of the respective strata, attention was directed to other 

 points illustrating the general object of this work. 



Trap Rocks. 



Having thus, from an acquaintance with similar deposits in other tracts, been able to 

 convey to the reader a sketch of the succession of the stratified masses, exhibited at cer- 

 tain points in this district, I now proceed to offer a few remarks on the intrusive rocks 

 which are associated with these deposits. 



The trap rocks rise to the surface amid the Silurian strata, and repeated examina- 

 tion has convinced me, that they have everywhere been forcibly intruded into the 

 latter. Though this view is opposed to that of the author who first described this 

 district, it is supported not only by the recorded opinion of Messrs. Buckland and 

 Conybeare, but also by that of nearly every geologist with whom I am acquainted, 

 who has visited these localities. In their forms, arrangement, and relations to the 

 associated strata, the trap rocks of Tortworth are entirely unlike any of those stratified 

 traps which have been described in this volume, and which alternate so equably and 

 conformably with the strata containing shells, as to afford sufficient evidence of having 

 been evolved during the accumulation of the marine deposits, (pp. 269 et seq. 325 et 

 seq.) On the contrary, these Tortworth trap rocks, whether viewed upon the natural 

 surface, or in any of the numerous quarries in which they have been laid open, consist 

 almost exclusively of amorphous masses, of irregular shape and unequal thickness, 



1 A recent widening of the road from Falfield to Tortworth, made by Dr. Cooke, exposed one of these little 

 arches of sandy grit and slaty marl, rising from beneath the adjoining beds of Wenlock limestone. This evi- 

 dence, however, was speedily obliterated by the building of a wall. Geodes of sulphate of strontian occurred 

 in this section. Their presence in the New Red Sandstone has been previously noticed. 



