﻿I860.] 



SALTER BOLIVIAN FOSSILS. 



63 



Of the Carboniferous forms little need be said. They are the same 

 as those described long ago in D'Orbigny's large work ; and similar 

 specimens were brought home by Mr. J. dimming during his ex- 

 plorations for recent shells in Bolivia. The resemblance to British 

 fossils of this epoch is most striking, and some of the species are 

 identical. 



The Devonian gives us very scanty traces, yet scarcely doubtful. 

 Occurring, as it does, between the Carboniferous basin and the slate- 

 rocks, it falls naturally into the place indicated by the few fossils 

 known to us. Mr. Pentland brought home from Aygatchi, in Bolivia, 

 a Trilobite from this formation. 



The age of the slate-rocks, however, was for a long time doubt- 

 ful ; and the aspect of Mr. Forbes's collection is so unlike that of 

 any British or American type, that, while their discoverer was 

 strongly urging their Silurian age, my own prejudice gave them 

 a Lower Devonian character. The large Homalonoti (the only con- 

 spicuous Trilobites) are, on the whole, more like Devonian forms 

 than Silurian ; and the shells are of just such types as might be 

 referred to either of these systems. The Tentaculites would bear the 

 same interpretation ; but a small Beyrichia, very rare, occurs just at 

 the top of the whole series, and this particular form of the genus is 

 not known in Europe to trespass beyond the Uppermost Silurian 

 limit, or the basement-beds of the Devonian at furthest. Again, 

 the Bilobites (whatever these obscure fossils may be) are all of 

 Silurian age, and they are numerous in Mr. Forbes's collection. 

 They have generally been regarded as Lower Silurian forms, and 

 are, indeed, far more plentiful below the Caradoc rocks than else- 

 where. But too much stress must not be laid on this ; for one cha- 

 racteristic species occurs in the Llandovery or Clinton group of New 

 York ; moreover, all the specimens from the Andes, whether the 

 large ones described by D'Orbigny, or the smaller ones now brought 

 home, are of species distinct from those known in other districts. 

 I do not believe them to be plants, but have no definite idea of their 

 true structure, further than that they were tough hollow crusts, not 

 soft solid masses as sea- weeds generally are. 



One other remark before proceeding to notice the separate species. 

 Wherever we meet with new areas of Silurian rocks, we find we have 

 in them new Natural-history provinces of these old seas : it is so in 

 India, according to Colonel Strachey's researches ; and it is so in Au- 

 stralia : no species from either region is, I believe, identical with those 

 of Europe. The same cannot be said of the Devonian fossils, which 

 ranged very widely during the later part of that epoch ; and the 

 Carboniferous types are almost cosmopolitan, many of the same 

 fossils ranging from the North Pole to Australia, and from North 

 America and the Andes to Nepaul. It is, I think, chiefly due to 

 this circumstance that we have been accustomed to regard the 

 Palaeozoic types as having an almost universal diffusion. This is 

 nearly true as regards the genera, but, except in the remarkable 

 case of the Mountain-limestone fossils, without much evidence in 

 the case of species. 



