449 



information. I rejoice to see this powerful geologist once more be- 

 fore us as an author, and still more when it is announced, in this last 

 useful work, that a series of figures, including all the un described 

 species of the shells of the Wealden formations, will appear in the 

 volume of the Geological Transactions now in the press, with a com- 

 prehensive Memoir upon the formations between the chalk and the 

 oolites, the publication of which has been so loudly called for by fo- 

 reign and native geologists. 



The results of my own observations during the last two summers 

 are about to be offered to you, in a detailed description of the upper 

 fossiliferous grauwacke, and its relations to the overlying deposits, 

 with descriptions of the intrusive rocks by which the series has been 

 penetrated. The zone examined, comprehends the western parts of 

 Shropshire and Herefordshire, and passing to the south-west, through 

 Radnor and the wildest tracts of Brecknockshire, terminates in the 

 mouth of the Towey in Caermarthenshire. As considerable spaces 

 within this zone have not yet been laid down for publication in the 

 Ordnance map, it is obvious that without the extraordinary aid, which 

 has been so cheerfully afforded me by Capt. Robe, and other officers 

 of His Majesty's Map-office, and also by that excellent field surveyor 

 Mr. Budgin, little progress could have been made in the performance 

 of a work, which, when completed, will I trust meet with your appro- 

 bation *. 



In the communication explanatory of these coloured maps, 1 hope 

 to prove that the old red sandstone, with few exceptions, passes 

 down into, and is conformable to, those rocks, to which we have been 

 accustomed to apply the term "Transition 5" and that, throughout great 

 areas, the old red sandstone is equally conformable to the overlying 

 carboniferous limestone as to the underlying grauwacke ; — that the 

 fossiliferous grauwacke is divided into a number of large natural for- 

 mations or groups, charged with a variety of organic remains, for the 

 most part undescribed. In tracing the lines of disturbance which 

 have affected these deposits, flexures upon a gigantic scale will be 

 pointed out, whereby the old red sandstone has been thrown into 

 basins of elevation, and, by a reversed inclination, extended to the 

 westward, far within the escarpment of the grauwacke ; and these lines 

 of disturbance and elevation will then be delineated, and their re- 

 lation traced to ridges of intrusive rocks. 



Whatever merit these observations may possess, they cannot but 

 derive value from being linked with the contemporaneous investigations 

 of Professor Sedgwick, amid the adjoining regions of grauwacke, 

 slate, and older rocks of the Welsh mountains. 



This will become evident when the Professor shall exhibit to you 



* This memoir owes the most valuable portion of its zoological illustra- 

 tions to the Rev. T. Lewis of Aymestrey. Colonel Wingfield, Dr. Dugard, 

 the Rev. I. Rocke, Mr. Jones, and Dr. Lloyd, have also contributed to throw 

 light on the structure of their respective neighbourhood in Shropshire. The 

 last gentleman has been fortunate enough to discover the remains of Tri- 

 lobites in the old red sandstone. 



( 

 \ 



