230 Geological Society. 



The above six deposits are all exhibited in Shropshire, trending 

 from N.E. to S.W., and occupying distinct ridges and valleys. In 

 their further prolongation to the S. W. the upper Ludlow rock is 

 uniformly persistent. Strata lithologically similar and containing 

 the same fossils are found invariably to rise from beneath the old red 

 sandstone in the counties of Hereford, Radnor, Brecknock, and Caer- 

 marthen ; sometimes at very low angles of inclination, while at others, 

 as in the promontories near Ludlow and Brecon, they are thrown up 

 into saddles, and at the south-western limit of Brecknock and Caer- 

 marthen shires they are vertical or very highly inclined. 



The second deposit, or Wenlock (Dudley) limestone, thins out a 

 little to the S.W. of Aymestrey, and the groups 1 and 3 being brought 

 together, generally occupy the same lofty escarpment in their course 

 through S. Wales. Hence the author suggests the term Ludlow for- 

 mation (the upper and lower Ludlow rock being subordinate mem- 

 bers), as applicable to all the higher portion of this series which has 

 a tripartite character in Salop and Hereford, due to the interpola- 

 tion of the Wenlock and Aymestrey limestone. 



The deposits 4?, 5, and 6, are three separate formations, entirely 

 differing from each other, and from the Ludlow formation, in their 

 characters, mineral and fossil, and in the distinctness of their phy- 

 sical demarkations. They are not, however, to be traced continu- 

 ously in their course from Shropshire on the N.E. to Caermarthen- 

 shire on the S.W.; though they reappear at intervals on that strike, 

 preserving their relative places in the geological series. 



In those districts where parallel ridges of all these formations are 

 brought to day within a zone of small breadth, rocks of trappean 

 or igneous origin are usual accompaniments, as in the neighbour- 

 hoods of the Wrekin and Caer Caradoc, in Shropshire j and again, 

 after a long interval, in the environs of Old Radnor, Builth and 

 Llandegley. In the intervening and featureless tracts of Clun, 

 Knuckless and Radnor forests, where such intrusive rocks are ab- 

 sent, the Ludlow formation alone is spread out in undulating masses, 

 and upon its surface are frequently found detached and elevated 

 basins of old red sandstone. 



The heights of the different groups above the sea-level vary from 

 500 to 2000 feet. 



The author reserves for the third part of his memoir, which he 

 proposes to communicate on a future occasion, the description of 

 the numerous trappean and porphyritic rocks, which, in penetrating 

 through these grauwacke deposits, have produced changes in their 

 mineral aspect and structure. On that occasion the question of the 

 parallelism of these sedimentary groups will be reviewed in reference 

 to the direction of the outbursts of rocks of igneous origin. The 

 quartz rock on the flanks of the Wrekin and Caer Caradoc, and also 

 in the singular ridge of the Stiper Stones, will be described under 

 the head of" Altered Rocks." The relations of the formations on 

 the eastern side of Herefordshire will also be explained, with the 

 view of determining whether deposits of the same age and charac- 



