324 BRACHIOPODA OF THE 



Lingula Lesueuri, Z. Haickei, L. Salteri, and Binobolus Brimonti, never contained any 

 other forms ; and that in the pebbles of the age of the " Gres de May " Caradoc species 

 only occurred with Orthis Budleij/hensis, the most abundant form of that division of the 

 Lower-Silurian formation. This opinion was subsequently confirmed by several com- 

 petent observers, among whom we may name Messrs. Salter, Linwood, Wyatt-Edgell, 

 Pengelly, Etheridge, J. T. Hall, de Tromelin, and others ; and on the 19th of July, 1879, 

 Mr. Vicary writes me, " I have never seen Silurian and Devonian forms in the same 

 stone." 



In 1869 I stated that the quartzites and sandstones, whether Devonian or Silurian, 

 differed so little, if at all, in composition and colour that unless the pebbles contained 

 fossils it was impossible to separate those belonging to the two periods. While writing 

 my paper in 1869 for the Exeter Meeting of the British Association, I found it out of my 

 power to class with certainty several new species occurring in the pebbles when they 

 were unaccompanied by any known species. I am still under the same uncertainty with 

 respect to some few of them ; but with regard to others, known species having been found 

 along with one or more of them in the same pebble, it has been possible to assign to 

 them their correct geological position. In that paper I described and figured thirty- 

 five species of Brachiopoda, and only a very few more have been discovered since that 

 period. 



Mr. Salter, with whom I often conversed upon the subject, was always under 

 the impression that the pebbles had been drifted from Normandy and Brittany, or 

 from between those regions and South Devonshire. 



After the reading of my paper to the Geological Society of London in 1869, 

 Mr. Etheridge observed that he assigned the rocks from which the pebbles had been 

 derived to the Hangman (Devonian) group of North Devon ; and that at Ansley Cove 

 Mr. Tawney had lately found a series of the same class of fossils in a matrix exactly 

 similar to that of the pebbles. Again, in 1870, in the discussion that followed the 

 reading of Mr. A. E. Ussher's paper, Mr. Etheridge said that he had been able to 

 ascertain, from specimens in the Penzance Museum, that the Budleigh pebbles (the 

 Lower-Silurian ones) came from Gorran Haven, on the south coast of Cornwall, and that 

 Orthis redux (our 0. Budleighensis, not 0. redux of Barrande) was common among the 

 specimens at Penzance. Mr. Whitaker on the same occasion observed that he himself, 

 on lithological grounds, suggested Gorran Haven as the source of the Budleigh- 

 Salterton pebbles. 



It was quite natural that British geologists should desire to find on British soil the 

 rocks, in situ, from whence the " pebbles " had been derived ; and that they thus should 

 also prefer to find a visible source, rather than search for it either in Normandy or 

 in the mid-Channel between Erance and Devonshire. 



We will, for convenience, discuss each hypothesis separately : 



1. The supposed British Devonian source; 



