152 J. S. Gardner — Correlation of the Tertiary Series. 



there is the gap in the sequence there which their present reference 

 to Upper Bagshot implies. 1 



The Bracklesham beds have a very considerable extension in the 

 Paris area, where they are universally admitted to be represented 

 by the well-known and important Calcaire-Grossier formation. It 

 is quite otherwise with the supposed Belgian equivalents — the 

 Bruxellien system. In this it is a question of averages, and out of 

 the list of twenty-seven of the most characteristic species cited 

 by Prestwich 2 to support the correlation, twelve, a very large 

 proportion, are Barton ; and the Mollusca, as a group, is not 

 sufficiently or purely Bracklesham to warrant belief in so northern 

 a spread of that formation. 



The Bovey Tracey Beds. — So ample an account of these and 

 their bibliography is to be found in the reprint from the Philosophical 

 Transactions, part iii. 1862, of the work upon them by Pengelly and 

 Heer, that little can now be added. The peculiarities in the biblio- 

 graphical history of these deposits are, first, that they were 

 frequently under the notice of scientific men for more than a 

 century, without any distinct vegetable-remains other than wood 

 being found in them; and, secondly, that the fact of Pleistocene 

 deposits overlying them led all writers to presuppose that they were 

 of very recent age. Before, however, Heer and Pengelly had 

 commenced work, Dr. Falconer " made several visits to Bovey," 3 in 

 some of which he was accompanied by other geologists. " The result 

 was a strong impression that the deposit would be found to belong 

 to the Miocene period." This impression was fully shared in by 

 Pengelly, who was gratified to find it borne out by Heer, when, upon 

 the determination of forty-one species, twenty-two of them new to 

 science, he pronounced the formation to be "decidedly of the Lower 

 Miocene age." 4 Time has, however, completely refuted upon plant 

 evidence the theory that the Bovey beds are Miocene, and unmis- 

 takably identified them with the Middle Bagshot of Bournemouth. 

 Upon geological evidence, also, the improbability is apparent of such 

 great deposits being accumulated in a Devonshire valley without 

 any trace of them existing elsewhere ; and a theory which brings 

 them into a defined position in the consecutive formations of the 

 country should be a welcome one. 



Pengelly's principal section shows a series of beds 115 feet thick, 

 allowing 10 feet for newer deposits, and at p. 14 we find that there 

 are at least 130 feet of underlying beds of the same age (99 feet 

 by actual section, and about 40 feet by estimate, less 10 feet for 

 surface Head or Pleistocene deposits) ; and we thus have a thickness 

 of some 240 feet. This by no means represents the total thickness, 

 for the bottom has never been reached, and there is also evidence 

 of great denudation. There is besides, a fault, which Pengelly 

 considers to show a vertical displacement of 100 feet, but which 

 may indicate more, to judge from a section on the east side of it, pos- 

 sessing, as it does, only an aggregate of 2 inches of coal instead of 

 36 feet in a similar depth, so that a great gap may exist between 



1 Mem. Geol. Surv. vol. vi. 1871, p. 333. 2 Q. J. G. S. vol. xiii. p. 106. 



3 Phil. Trans, part iii. 1862, p. 3. * I.e. p. 18. 



