T. Davidson — Tertiary Brachiopoda. 361 



frankly admit that there are so many inexplicable sudden appear- 

 ances of entirely distinct forms, with no apparent links, connecting 

 them with those that were antecedent, or even contemporaneous, 

 that it is impossible, in the present state of our knowledge, to 

 arrive at any definite conclusions. To what extent species are 

 derived from their predecessors, is a problem which may, or may 

 never be completely explained, but it is so sublime a subject of in- 

 vestigation, that every new fact acquired is of the highest value to 

 the intellectual observer. 



It will not be possible or necessary here to enter into any 

 lengthened discussion relative to the views entertained by different 

 geologists in connection with the number of stages into which the 

 Tertiary period should be divided, or as to the names which each of 

 these should retain ; but we cannot go far wrong in grouping the 

 Italian Brachiopoda into the following well-known divisions :— 



Eecent. 

 Quaternary. 

 C q ( Upper Pliocene. 

 j I Lower Pliocene. 

 Tertiary J ( Upper Miocene. 

 period. ^ 2 | Middle Miocene. 

 ( Lower Miocene. 

 ^ 1 Eocene or Nummulitic. 

 Cretaceous (Scaglia of the Italians). 

 We may, however, mention, prior to entering upon the main sub- 

 ject of this communication, that in his " Tableau Synchronistique des 

 Terrains Tertiaires,^'' published in 1868 and 1869, Mr. Ch. Mayer, of 

 Zurich, has divided the Tertiary period into the following fourteen 

 separate stages : — 



^ XIV. Etage Saharien = Saharian series, 1865. 

 I' XIII. Etage Astien = Astian series, 1856. 

 ■•^ Xn. Etage Messinien = Messinian series, 1867. 

 H \ XL Etage Tortonien = Tortonian series, 1867. 

 1^ X. Etage Helvetien = Helvetian series, 1857. 



^ IX. Etage Langhien = Langhian series, 1866. 

 l^Vni. Etage Aquitanien = Aquitanian series, 1867. 

 '' VII. Etage Tongrien = Tongrian series, 1852. 

 VI. Etage Ligurien = Ligurian series, 1857. 

 V. Etage Bartonien = Bartonian series, 1857. 

 H \ IV. Etage Parisien = Parisian series, 1857. 

 I III. Etage Londonien = Londonian series, 1857, 

 ° II. Etage Soissonien = Soissonian series, 1857. 



l^ I. Etage Flandrien = Flandrian series, 1868. 

 The Eocene deposits of the North of Italy have been carefully 

 studied by several geologists ; but, from want of space, I must refer 

 the student for details upon this subject to the admirable memoir by 

 Dr. Suess, pubhshed in the Proceedings of the Italian Society of 

 Natural Sciences for the Meeting held at Vicenza, Venetia, in 1869, as 

 well as to M. Bayan's excellent paper on the " Terrains tertiaires de 

 la Ven^tie," published in the Bulletin of the Geological Society of 



