44 Geological Society. 



variance with a surmise I ventured to advance last year respecting the 

 age of the lithographic stone of Solenhofen. That comparison was 

 intended simply to afford the English geologist an approximate idea 

 of the age of a rock, which, by some of my countrymen, had been 

 considered as of tertiary origin, by others, as belonging to the green- 

 sand ; so that if my rough estimate should prove less accurate than 

 that of a distinguished Prussian *, who has since compared it with the 

 coral rag, I shall still feel satisfied in having first pointed out to the 

 English inquirer, that the Solenhofen slate is a member of the Ju- 

 rassic or oolitic system, and that, from the general similarity of many 

 of the organic remains, such as Pterodactyli, Crustacese, and certain 

 plants, it is probably the equivalent of the Stonesfield slate, or one 

 of the central and slaty members of this complex series. On a broad 

 scale, however, I feel persuaded, that a simple division into "upper" 

 and ft lower" oolitic systems is the full extent to which we can bring 

 continental and British formations of this age under comparison. 



To Dr. Fitton we are indebted for his " Notes on the Progress of 

 Geology," in which the relative merits of the founders of the science 

 in England are well put forth -, and also for his " Geological Sketch 

 of the Vicinity of Hastings," a most valuable addition to those local 

 monographs which contribute so largely to the diffusion of precise 

 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 undescribed 

 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 f. 



* Von Buch. 



f 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 neighbourhoods in Shropshire. The 

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

 Jobites in the old red sandstone. 



