BRITISH SILURIAN BRACHIOPODA. 65 



^Tarannon shales. 



Denbighshire grit. 



Woolhope beds. 

 Upper Silurian. *( Wenlock beds. 



Lower Ludlow. 



Aymestry. 

 LUpper Ludlow. 



At p. 60 of his Address Mr. Etheridge, alludes to Mr. Lapworth having proposed a 

 tripartite division of the Lower-Palseozoic rocks^ and having suggested the name 

 Ordovician for all that group of strata, in the Bala district, to which Murchison had 

 previously applied the name of Loioer Silurian, and Sedgwick that of Tipper Cambrian. 

 I can see no advantages in substituting the synonym Ordovician for the well-known 

 name Lower Silurian adopted by the Survey and by far the larger number of geologists, 

 at home as well as upon the Continent. 



Since 1871 I have never ceased to be on the look-out for every new species that occa- 

 sionally turned up, and in improving my knowledge of those already described. Very 

 much in this respect remained to be discovered in 1871, and no doubt very much more 

 will have to be found out after this Supplement shall have been published, for science is 

 continually on the advance. I am, however, pleased to be able to state that the larger 

 proportion of our British Palaeozoic Brachiopoda is now well understood, and has been 

 properly described, figured, and classed ; but there still remains a certain number of these 

 that cannot yet claim that advantage, and it is only with more time and with continued 

 research under favorable circumstances that those uncertain or doubtful so-termed species 

 can be definitely determined and placed in their proper genera and families. All we can 

 do is to offer our present knowledge of the subject. 



Shropshire was always considered by Sir Roderick Murchison as one of the districts 

 in which his Upper- Silurian rocks could be most advantageously studied ; and it therefore 

 occurred to George Maw, Esq., F.G.S., of Benthall Hall, Shropshire, and to myself, that 

 some valuable results might be obtained by washing some twenty or more tons weight of 

 Wenlock and Ludlow shales taken from different places and at different horizons. This 

 expensive and great undertaking was generously and thoroughly carried out by Mr. Maw, 

 who at the same time had the old quarries of Benthall Edge and Wenlock carefully hand- 

 picked for specimens. These laborious operations have brought to hand some 50,000 or 

 60,000 specimens, some being new to science, while others are better represented than 

 previously. 



At my request, in 1880, Mr. Maw kindly forwarded to me the following notes in 

 connection with his washing operations, along with some few remarks on the physical 

 character and thickness of the Upper-Silurian rocks of Shropshire.' These observations 



^ These notes were published in the ' Geological Magazine,' New Series, vol. viii, p. 100, March, 



