Ixx' PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



continued deposition of sedimentary masses of such enormous thick- 

 ness as those we are considering. 



If we turn now to the district lying on the east and south-east of 

 the hue of Trappean eruption from Builth to the LongmyncI, we find 

 the same conformity between the Upper Silurians and the Old Red 

 Sandstone, wherever the latter exists, and in the eastern part of the 

 S. Wales coal-district, we have the same conformity, as ia the western 

 part, between su^perincumbent formations up to the Coal-measures. 

 Further to the north, in the Shropshire coal-fields, the Old Red Sand- 

 stone does not exist, and the Carboniferous Limestone, where it exists, 

 reposes immediately on the Silurians, on which also the Coal reposes 

 in the absence of the Carboniferous Limestone ; but in these cases the 

 stratification of the Silurians and superincumbent limestone or coal- 

 measures is always, or very generally, decidedly discordant. On 

 these points excellent details and sections are given by Sir Roderick 

 Murchison in his Silurian System. I am not acquainted with the 

 details of supei'position in Denbighshire. 



In the North of England the break between the Upper Silurians 

 and the superincumbent beds is very decided. There the beds of 

 Carboniferous Limestone are observed in many places to he, with a 

 comparatively small inclination to the horizon, on the highly inclined 

 Silurian beds. No discontinuity, however, has been there observed 

 corresponding to that belonging to the period of the Caradoc Sand- 

 stone in Wales. 



The next great discontinuity which exists in the stratification of 

 the Palseozoic rocks both in Wales and the adjoining districts, and 

 in the North of England, is that between the Coal-measures, speaking 

 generally, and the superincumbent beds. In the West of England, 

 Sir Roderick IMurchison has ascertained that, in several localities, the 

 Coal-measures graduate into the lowest Permian beds. In the North 

 of England, on the contrary. Professor Sedgwick has observed the 

 lowest Permian beds of that region resting unconformably on the 

 Coal strata; and the same is true with respect to the Dolomitic Con- 

 glomerate of the neighbourhood of Bristol and the south-eastern part 

 of the coal-basin of South Wales. There are also discontinuities 

 between different portions of the Permian and Triassic groups which 

 will be more particularly discussed as we proceed. They are im- 

 portant with respect to the history of the movements, the efl"ects of 

 which are so striking in the Coal-measures. 



In tracing the history of those revolutions of the globe in which 

 the above discontinuities of stratification have arisen, it appears to 

 me necessary to bear distinctly in mind three different kinds of ter- 

 restrial movements : First, those great movements which, extending 

 over comparatively wide areas, have dislocated the strata, and left 

 them inclined in a greater or less degree to their original horizontal 

 positions, thus producing anticlinal lines, faults, and other phseno- 

 mena of elevation throughout the whole district in which the move- 

 ments have taken place. Such movements mayor may have not been 

 accompanied with outbreaks of igneous matter, such outbreaks, when 



