SUPPLEMENT 



BRITISH SILURIAN BEACHIOPODA, 



The first part of my 'Silurian Monograph' was published in December, 1866, 

 the fifth and concluding part in January, 1871 ; and, although I had then devoted 

 fully six years to the study of the Cambrian and Silurian Brachiopoda of Britain, I 

 felt that very much more material would be forthcoming with time and continued 

 research. Now, as expected, I have very much more to add to what I had so far 

 completed in 1871. 



Changes and improvements have been effected from time to time in the subdivision of 

 the Cambrian and Silurian systems ; but it is not my province, in the pages of the Palgeon- 

 tographical Society, to enter upon any lengthened detail or discussion with respect to 

 the geology of the Lower-Palseozoic formations, beyond assigning to each species its 

 proper place and range. In the main I still adhere to Sir Roderick Murchison's classifi- 

 cation, as he was the first to establish his divisions as " identified by organised fossils," 

 thus carrying out the principles so ably laid down by William Smith in 1816. What- 

 ever may be said to the contrary, I firmly maintain that it is to Sir Roderick's 

 exertions, continued research, travel, and influence, that the study of the Lower 

 Palaeozoic rocks and fossils was so successfully spread over the whole of Europe and 

 America.^ 



Changes were no doubt necessary to perfect the classification propounded by Sir 

 Roderick Murchison in his 'Silurian System,' published in 1839, and Sir Roderick 

 himself was fully aware of that necessity as the result of continued research; and 

 he himself proposed alterations in his own classification in his subsequent work, 

 ' Siluria.' 



I am far from wishing to undervalue the very valuable and important researches of 

 the Rev. Adam Sedgwick ; but it is much to be regretted that that eminent geologist left, 



^ See Mr. Barrande's important paper "Du Maintien de la nomenclature etablie par Mr. Murchison," 

 'Congrfes International de Geologie,' p. 101, Paris, 1878. 



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