Vol. 70.] THROUGH THE ANDES OF PERU AND BOLIVIA. 31 



the sequence and the position of the two important outcrops of 

 limestone (see diagrammatic section, p. 30). 



The Straits of Tiquina, which form a narrow passage about half 

 a mile wide between the northern and southern portions of the lake, 

 lie along the axis of a steeply-folded syncline of red sandstone and 

 breccia, faulted on its eastern side against Devonian quartzites and 

 underlain conformably on the west in the peninsula of Copacabana 

 by yellow and black shales, which dip 60° north-north-eastwards. 



The latter are succeeded by a thick outcrop of grey chert v lime- 

 stone, containing numerous examples of Euphemus, Spiriferina, 

 and Semimda : the last-named occur chieflv in the form of silicified 

 casts showing the internal spires. Towards the summit of the hill 

 above San Pedro a second and lower limestone appears, which is 

 characterized by Productus eora and Sjririfer condor. The dip 

 here changes to a westerly direction, and the beds appear to form 

 the summit of a normal anticline. 



From this locality David Forbes obtained the series of fossils 

 afterwards described by J. W. Salter. 1 



In addition to my own specimens, I have examined a number 

 of Carboniferous fossils brought back from Bolivia bv other 

 travellers ; these are preserved in the British Museum (Natural 

 History), and by the kindness of the Trustees I have been enabled 

 to incorporate them in my description of the formation. Some are 

 of interest as coming from A. d'Orbigny's type-locality of Yarbi- 

 chambi between Huarina on Lake Titicaca and La Paz; others are 

 from Yampupata on the Copacabana peninsula, as also from Arque, 

 a locality farther south in the Oruro district. 



Most of the specimens that I have examined appear to belong to 

 an Upper Carboniferous or Pernio- Carboniferous fauna, showing 

 affinities with types described by Chernyshev from the Urals; while 

 a few seem more nearly related to Permian forms figured by Waagen 

 from the Salt Kange of India, and by Grirty from the Gruadalupian 

 fauna of New Mexico. The evidence for this comparison, which is 

 more fully stated below, points to the fact that the true fossiliferous 

 Lower Carboniferous (or Avonian) of Europe is not represented, or 

 remains undiscovered, in this region of Southern Peru and Bolivia. 



Faunal List. 



Spirifer condor D'Orb. Scabriculocostate Productus — Pr. 



Spiriferina aff. cristata Schloth. inca D'Orb. 



Semimda ambigua mut. (Sow.) = S. Enteletes aff. hemiplicata Hall. 



peruviana (D'Orb.). ] Rhipidomella sp. 



Productus cora D'Orb. Derbya sp. 



Productus aff. spimdosus J. Sow. Hustedia sp. 

 Productus semireticulatus mut. 



Mart. Euphemus cf. indicns Waagen. 

 Productus antiquatus mut. Sow. 



1 Q. J. G. S. vol. xvii (1861) p. 64 & pi. iv. 



