1 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



name of Himantopterus. There are five or six species of this genus, 

 all of which are new, and one of which, judging from the head, which 

 is alone preserved, must have been 3 feet in length. 



With reference to this subject, I must also notice a paper by 

 Mr. R. W. Banks, communicated to us by Sir R. Murchison, " On 

 the Tilestones orDownton Sandstones in the neighbourhood of King- 

 ton, and their contents." Besides describing the geological sequence 

 of these beds, and noticing the fossil contents by which they are 

 principally characterized, and which are remarkable for the abun- 

 dance of crustacean remains, the author exhibited some highly- 

 finished drawings of the organic remains. These, together with his 

 descriptive notes, indicated the existence of one or more hitherto 

 unknown or little understood forms of crustacean life, probably of 

 the Eurypteridse group. Without going further into the question of 

 other forms of organic life contained in these beds, there appears to 

 be every reason for concluding that this Tilestone formation is, as 

 was stated by Sir Roderick Murchison, the equivalent of the fossili- 

 ferous band which underlies the coal-field of Lesmahago. In con- 

 cluding his paper, Mr. Banks says, — " From the absence of the nu- 

 merous Mollusca characteristic of the Ludlow rocks, and from the 

 presence of Crustacea that have not been found in the Ludlow beds, 

 and especially from the abundance of the Fterygotus, so characteristic 

 of the middle Old Red of Scotland, I am inclined to separate these 

 Downton or Tilestone beds from the Upper Ludlow rocks, and class 

 them (as Sir R. Murchison originally arranged them) as the bottom 

 beds of the Old Red Sandstone." 



Here we have a remarkable instance of that difficulty to which I 

 alluded in my Address last year, — a difficulty which increases as our 

 knowledge of geological formations increases. With each advancing 

 step it becomes more difficult to draw precise limits between suc- 

 cessive formations. The following words would almost seem to have 

 been written in anticipation of the question under consideration : — 

 " It has been found that between these respective limits, as at first 

 laid down, certain fossils of the lower bed extend higher up into 

 those above ; while some of those hitherto supposed to be charac- 

 teristic of the overlying formation are found extending downwards 

 into beds of an older age." The same idea has been more fully 

 and more clearly expressed by Sir Charles Lyell, in his last edition 

 of the * Manual of Elementary Geology.' He says (chap. x. p. 112), 

 " The difficulty of assigning clear lines of separation must unavoid- 

 ably increase in proportion as chasms in the past history of the globe 

 are filled up." 



Now, in the case before us, while on the one hand Sir Roderick 

 Murchison is prepared to regard these Lesmahago flag-like schists, 

 chiefly on the evidence of their fossil contents, as separate from the 

 Old Red Sandstone series, and to class them with the Upper Ludlow 

 beds, Mr. Banks, on the other hand, equally arguing on fossil evi- 

 dences, proposes to remove the equivalent Tilestones or Downton 

 Sandstones from the Upper Ludlow rocks, and to class them as the 

 bottom beds of the Old Red Sandstone. Under such circumstances. 



