DOLOMITIC CONGrjOMKHATE OP BBTSTOL. 



209 



composed chiefly of fine crystals, very yellow in colour, and 

 which crumbled into a fine crystallized sand on being cast 

 out on the tip. North of Bristol, the Dolomitic Conglomer- 

 ate is not so largely developed, even against the Limostone 

 ridge running from Olvcston, via Wickwar, to Chipping 

 Sodbury ; and is only found in small detached portions, ex- 

 cepting near Tliorrdjury, whore there is a considerable area 

 lying partly against the Old lied Sandstone, and partly 

 against the Carboniferous Limestone. A peculiarity here is, 

 that yoir have a clear way from the Severn Alluvium to the 

 Dolomitic Conglomerate without passing over the Keuper 

 Marl, and that, passing in a south-easterly direction, the 

 strata alternate from Dolomitic Conglomerate to Old Red 

 Sandstone, Dolomitic Conglomerate,, again, then Old Rod 

 again, from that passing on to the (carboniferous Limestone, 

 after which the Dolomitic Conglomerate again appears, 

 succeeded by the Keuper Marl. 



The Dolomitic Conglomerate of our district is an eminently 

 local deposit. Tiiis is well seen in the road cut from the 

 Port and Pier Railway Station, under the Suspension 

 Bridge, to the Downs near Proctor's fountain, where blocks 

 are found of very large size, and weighing several hundred- 

 weight at least, showing that the source of suj)ply was 

 close at hand. These blocks chiefly consist of Carboniferous 

 Limestone and Millstone Grit, and arc embedded along with 

 small pebbles. 



A similar instance to that of I'atchway Tunnel, before 

 referred to, of the sudden rise of the Dolomitic Conglomerate 

 from a comparatively horizontal, position to a steep rise, is 

 shown in the section of the Severn Tunnel, published in the 

 last volume of the Proceedings of the Bristol Naturalists' 

 Society. There it is first met with at the bottom of No. 2 

 shaft, whence it passes, with a slight undulation about half 



