100 T. Davidson ^ O. Maic — IT. Silurian RoclxS of Shropshire. 



II. — Notes on the Physical Character and Thickness of the 

 Upper Silurian Rooks op Shropshire, with the Brachiopoda 

 they Contain grouped in Geological Horizons. 



By Thomas Davidson, P.E.S,, and George Maw, F.G.S. 



[Contimtedfrom p. 13.) 



SHROPSHIRE was always considered by Sir Roderick Murcliison 

 as one of the districts in which his Upper Silurian rocks could 

 be most advantageously studied.^ We propose, therefore, in this 

 communication to offer some few notes on the Geology and Paleeon- 

 tology of the Wenlock and Ludlow series ; illustrated by the 

 Brachiopoda, reserving for the present what we may have to com- 

 municate with respect to the Upper Llandovery. 



The extensive washings undertaken by one of us have brought to 

 light some fifty to sixty thousand specimens, of which some were 

 previously unknown, while others were new to the district. The 

 new species will be described and figured in the sequel. 



The occurrence of cleanly-washed fossils in the debris remaining 

 from many of the clays and shales suggested to one of us that the 

 potter's process of Igevigation might be conveniently employed by the 

 geologist for the collection of fossils, especially of the smaller 

 species, from the soft shales, in which hand-picking is at best a 

 most laborious process. 



The potter's object in clay lasvigation is to get rid of the coarser 

 matter. The fossil collector pursues, as it were, the process in 

 reverse by getting rid of all the clay and fine matter, and obtaining 

 in a compact form the coarse debris, including the organic remains. 



A potter's " Blunging " or clay laevigating machine, though it 

 greatly facilitates the process, and enables large quantities of 

 material to be quickly Itevigated, is not essential, as an experienced 

 worker can in a day easily laevigate several hundredweights of clay 

 or soft shale, with the aid only of a tub and a stout wooden stirrer. 



The operator should provide himself with a set of sieves of the 

 following mesh : 1, 2, 4, 6, 10 and 12 wires to the inch. 



Having digested in water, say, half a ton of material, the '•' slip " 

 or liquid clay is poured off through the No. 12 or finest sieve, wliich 

 would catch any small fossils ; and the remaining debris, which 

 might weigh about a hundredweight, should be repeatedly washed 

 with fresh water, by which all fine matter will be removed, and the 

 material remaining will in most cases resemble clean coarse gravel, 

 with which the operator will have further to deal. As this will 



^ "We follow Sir Eoderick Murchison's classification of the Lower Palaeozoic 

 formations, for no geologist worked harder to unravel the complications under which 

 the Upper and Lower Siliu-ian rocks were shrouded. The publication of the 

 " Silurian System" in 1839, with all its imperfections and on the model of Smith's 

 " Strata identified by Organized Fossils," did more than any other work to stimulate 

 researches in the right direction all over the world. See also Barrande's important 

 paper " Du maintien de la nomenclature etablie par Mr. Murchison," Congres 

 International de Geologic, p. 101, Paris, 1878. 



