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PBOCEEDIXGS OP THE GEOLOGICAL SOCIETY. 



[Nov. 21, 



racters very similar to the Lower Silurian series in Europe, particu- 

 larly as we do not, as far as I have examined, meet with the lime- 

 stone beds and calcareous shales generally accompanying the Upper 

 Silurian series. The examination made by Mr. Salter of the fossils 

 extracted by me from these beds appears, however, to show that we 

 probably have the whole Silurian series, from lower to upper, fully 

 represented, notwithstanding the general uniformity in mineral cha- 

 racter of the beds. 



Starting from the north, at Tipuani, we find this auriferous region 

 principally composed of blue clay-slates, which, from information 

 communicated to me, I believe to cover a vast area, extending down 

 to the River Beni. In these strata no fossils have as yet been found*; 

 but they appear to be quite continuous with the beds which contain 

 fossils near Sorata, about five miles south of which town I found, at 

 a small Indian place called CotaSa, on the east side of the river, an 

 Orihis (apparently 0. Aymara), Strophomena (species undetermined), 

 Annelid-tubes well defined, and small round bodies of pyrites with 

 a hole in the centre like the joint of an Encrinite, about one-third 

 of an inch in diameter, occurring in the blue slate f. 



Still further south, on the north-west slope of Illampu, I found in 

 loose stones, at a place called Cochipata, traces of Cruziana Unduavi 

 (PL Y. figs. 7, 8), and a little further, at TJcumarini, also on the east 

 side of the river, Annelid-burrows and the Cruziana Cucurbita (PI. V. 

 figs. 4-6). The burrows were of varied forms and sizes, and perfect 

 counterparts of those from Unduavi in Yungas, although this place 

 is situated some 120 miles distant on the other side of the Andes. 



Still further south I fixed my head-quarters in the Hacienda de 

 Millepaya, and by extensive excursions from that point, and ascents 

 as far as possible up the steep western slope of Illampu (or Sorata, 

 as it is generally but erroneously termed %, from the town of that 

 name situated at its base), I was enabled to form the section of the 

 strata represented in Section No. 1, and to examine the beds as to 

 their fossil contents. The results of this examination are given below, 

 premising that above the shales forming the uppermost beds repre- 



* It requires an attentive search in order to discover fossils in a new country. 

 The small number of Bolivian fossils at present known is not to be ascribed to the 

 poverty of the rocks, but to the insignificant proportion which the few isolated 

 spots hitherto examined bear to the vast area of this republic : as far as I have 

 explored, this country shows evidence of being eminently fossiliferous. I believe, 

 however, that I have, during my recent and short travels in this country, brought 

 home more fossils than any explorer before me, notwithstanding that M. D'Orbigny 

 and M. Pissis (who lived eight years in Bolivia) had much better opportunity 

 than myself. 



f I have to thank Mr. Salter for his great kindness in carefully examining the 

 fossils of the Silurian, Devonian, and Carboniferous series. The names here given 

 are those affixed by that gentleman, who has communicated a paper illustrative 

 of the fossils which I brought home from Bolivia. See p. 62. 



\ The mountain itself is called in Bolivia by the original name of Illampu, at 

 the foot of which, to the north, the town of Sorata is situated ; and the snowy 

 range above this town being frequently called the " Nevados de Sorata " has led to 

 the mountain Illampu (the highest peak of this range) being called, more parti- 

 cularly by English writers, Sorata. 



