CLASSIFICATION OF THE SILURIAN ROCKS. 29 
Museum to contain the national type collection of Britain, Mr. Davidson has figured, in 
every instance, those specimens which are most truly characteristic, including also many 
of the oldest types, collected by myself, and now preserved in the Museum of the Geological 
Society. He thus affords to the student, and mainly through the assistance of our able 
Paleontologist, Mr. Etheridge, a ready means of comparing any species he may collect 
with the fixed species in the geological museum of the nation. Thus, along with other 
works in the field and the closet, this Monograph, and the beautiful fossil forms found 
in our own country—all drawn by the hand of Mr. Davidson—will remain as illustrations 
of the truthfulness of our national geological maps, as prepared after a careful correlation 
of the order of the strata with their imbedded animal remains. 
From his long residence in France, as well as in other parts of Europe, and his inti- 
mate acquaintance with the Palzozoic collections of M. de Verneuil and others, whether 
formed in Europe, America, or elsewhere, Mr. Davidson has happily had advantages which 
few of his cotemporaries have enjoyed; and when we reflect that the labour of so many 
years has, on his part, been one of true love of natural history science, all Geologists, 
feeling how much they owe to him, must unite with me in gratefully recording our 
sincere obligations. or myself, I cannot sufficiently express the gratitude I feel for the 
devotion, perseverance, and ability with which Mr. Davidson has fulfilled his great 
undertaking, thus crowning his many admirable works with a complete Monograph of 
the oldest known group of Fossil Brachiopods in the crust of the globe. 
P.S.—In the preceding pages 24 e¢ seg. the prevalent lithological characters only of the typical 
Silurian rocks of Britain have been given. The pebbly beds and conglomerates which occa- 
sionally occur are mentioned in the following table. 
