Ch. XXXII. ] eocene volcanic kocks. 695 



adjoins Monte Bolca. There is evidence here of a long series of 

 submarine volcanic eruptions of Eocene date, and during some of 

 them, as Sir B,. Murchison has suggested, shoals of fish were probably 

 destroyed by the evolution of heat, noxious gases, and tufaceous mud, 

 just as happened when Graham's Island was thrown up between 

 Sicily and Africa in 1831, at which time the waters of the Mediter- 

 ranean were seen to be charged with red mud, and covered with dead 

 fish over a wide area.* 



Associated with the marls and limestones of Monte Bolca are beds 

 containing "lignite and shale with numerous plants, which have been 

 described, by linger and Massalongo, and referred by them to the 

 Eocene period. I have already cited (p. 291) Professor Heer's re- 

 mark, that several of the species are common to Monte Bolca and 

 the white clay of Alum Bay, a Middle t\ocene deposit ; and the same 

 botanist dwells on the tropical character of the flora of Monte Bolca 

 and its distinctness from the subtropical flora of the Lower Miocene 

 of Switzerland and Italy, in which last there is a far more consider- 

 able mixture of forms of a temperate climate, such as the willow, 

 poplar, birch, elm, and others. All these are wanting at Monte 

 Bolca, while on the other hand the coniferae are represented by five 

 species of Podocarpus, the Dicotyledons by the fig and sandal-wood 

 tribe, and by some Proteacece. There are also many tropical forms 

 of Leguminosce, together with fan-palms, and a palm allied to the 

 cocoa-nut with its fruit ; also, according to Massalongo, an orchideous 

 epiphyte. That scarcely any one of the Monte Bolca fish should 

 have been found in any other locality in Europe, is a striking illustra- 

 tion of the extreme imperfection of the palseontological record. We 

 are in the habit of imagining that our insight into the geology of the 

 Eocene period is more than usually perfect, and we are certainly ac- 

 quainted with an almost unbroken succession of assemblages of shells 

 passing one into the other from the era of the Thanet sands to that 

 of the Bembridge beds or Paris gypsum. The general dearth, there- 

 fore, of fish might induce a hasty reasoner to conclude that there was 

 a poverty of ichthyic forms during this long period ; but when a local 

 accident, like the volcanic eruptions of Monte Bolca, occurs, proofs 

 are suddenly revealed to us of the richness and variety of this great, 

 class of vertebrata in the Eocene sea. The number of genera of 

 Monte Bolca fish is, according to Agassiz, no less than seventy- five, 

 twenty of them peculiar to that locality, and only eight common to 

 the antecedent Cretaceous period. Xo less than forty-seven out of 

 the seventy-five genera make their appearance for the first time in the 

 Monte Bolca rocks, none of them having been met with as yet in the 

 antecedent formations. They form a great contrast to the fish of the 

 secondary perio'd, as, with the exception of the Placoids, they are all 

 Teleosteans, only one genus, Pyc?iodus, belonging to the order of 



* Principles of Geology, chap, xxvi., 9th ed., p. 432. 



