40 MR. J. A. DOUGLAS ON GEOLOGICAL SECTIONS [vol. lxxvi, 



however, and it is more than likely that they were obtained from 

 the Devonian beds between Puno and Taya Taya. The following 

 forms are mentioned : — GrypJiceus convexus Ulrich, Platyceras 

 sp., Spirifer planoconveocus Knod, Lyopova gigantea Knod, and 

 crinoid-remains. ) 



Continuing northwards, we meet with a further series of beds 

 between Juliaca and Laro, apparently distinct from those above 

 enumerated, comprising olive-green quartzites, shales, and sand- 

 stones, which have a more or less constant dip in a south- 

 westerly direction. These are very similar in appearance to the 

 Devonian beds of Taya Taya ; and, in fact, a short distance farther 

 east, between Pusi and Taraco, the following fossils have been 

 recorded hj Senores Duefias & Romaha: — Phacops cf. dagincourti 

 Ulrich, Orthoceras sp., Gonularia sp., Tentaculiies sp., and 

 Tropidoleptus carinatus Conrad. 



An identical fauna has also been obtained from the neighbourhood 

 of Sicuani, a village still farther north on the line to Cuzco ; and, 

 as Tirapata lies directly between these two points, the barren 

 shales and shaly sandstones which are found at this .locality are 

 regarded on both stratigraphical and lithological grounds as being 

 of the same age. 



If we proceed, moreover, along the same line of strike far 

 towards the south-east, we eventually reach the Devonian area of 

 Tiahuanaco and Coniri in Bolivia. 



It will thus be seen that, although I rely in great part on the 

 lithological characters of the rocks in the determination of their 

 age, the conclusions arrived at are in no way contradicted by the 

 meagre palseontological evidence obtained at one or two isolated 

 localities. 



As we continue our journey north-eastwards from Tirapata, the 

 Devonian shales and impure sandstones are no longer inclined 

 towards the south-west, but are seen to dip in an easterly direction 

 beneath a strongly-folded series of grey limestones, dolomites, red 

 marls, and white quartzites. These rocks are well exposed along 

 the road to Progreso, and on the southern shore of the lake beyond 

 Asillo. 



At the hamlet of Recreo the trail turns northwards, following 

 the strike of the folds up a small river- valley cut along one of the 

 anticlinal axes. The beds here consist chiefly of conglomerates 

 and sandstones, with an occasional prominent band of grey lime- 

 stone. 



The river has its origin in a small lake (Lago Cerera), at the far 

 end of which we traverse the actual core of the anticline, here 

 seen to be formed of limestone overlain on the east by conglomerate 

 dipping 30° north-eastwards. 



This whole series of rocks, although well exposed and freely 

 accessible, failed to reveal any trace of fossils ; but there can be 

 little doubt that it represents the northward continuation of the 

 Carboniferous series of the isthmus of Copacabana and the Island 

 •of the Sun in Lake Titicaca. 



