part 3] SILURIAN ROCKS of the CLUN-FOREST DISTRICT. 245 



Discussion. 



Mr. W. Wihtaker asked whether there was any stratigraphical 



break between the Silurian and the Old Red Sandstone. 



Mr. Gr. W. Lamplugh, in commenting upon the attenuation of 

 the successive divisions in the same direction, enquired if the 

 character of the beds revealed whether they were deposited upon 

 an original slope, or upon a plane which was gradually tilted. 



Dr. A. Smith Woodward was surprised by the absence of 

 fish-remains among the fossils. It was important to make special 

 search for them, because they marked well the different horizons 

 at the base of the Old lied Sandstone, and even fragments were 

 often identifiable. 



Dr. J-. W. Eyans remarked on the importance of work on the 

 passage-beds between the Silurian and the Old Red Sandstone in 

 Shropshire. The present limits of the Devonian throughout the 

 world were primarily determined by those of the continental or 

 Old lied Sandstone conditions in this area. There was, however, 

 a difficulty in correlating the highest marine beds with those of 

 other areas, because not only did the horizon in all probability 

 vary from point to point, but the beds were laid down under 

 abnormal conditions. It was quite possible that they might be of 

 the same age as strata elsewhere (as, for example, in Belgium) re- 

 ferred to the Devonian by most authors. He enquired whether the 

 Old Red Sandstone was represented only by sandstones, or whether, 

 as was usually the case, the red marls were the most important 

 feature of the lower portion of the formation. 



Mr. R. B. Newton referred to the absence of Lingula cornea 

 and Ouchus-sp'mas among the fossils exhibited by the Author, 

 from the dun-Forest district, both of which are characteristic of 

 the uppermost division of Murchison's scheme of the Silurian 

 strata, as published in Davidson's ' Monograph of the British Fossil 

 Brachiopoda ' (I860) part 7: 'The Silurian Brachiopoda,' p. 30. 

 The occurrence of Lingula minima^ which is considered to differ 

 from L. cornea and to belong to a lower horizon, is, however, 

 observed in the Author's collection. The suggestion is made, 

 therefore, that the Clun-Forest fossils belong to the topmost part 

 of the Upper Ludlow, as stated by the Author ; but that the 

 deposits at Kington, Downton, etc., with Onchus and Lingula 

 cornea, would represent the passage-beds between the Silurian and 

 the Old Red Sandstone. 



Dr. A. H. Cox, replying on behalf of the Author, stated that 

 there was no indication of any stratigraphical break cither within 

 the Silurian rocks themselves, or between the Silurian and the Old 

 Red Sandstone. The fossil-bands of small individuals and also the 

 ' Fragment-Bed,' were merely due to slight changes in conditions, 

 such as changes in the salinity of the sea -water, but they did not 

 imply breaks in deposition. The Author devoted a section of his 

 paper to a discussion of the gradual oncoming of Old Red Sand- 

 stone conditions, the changes in lithology being in the main quite 



Q. J. G. S. No. 295. u 



