part 3] THEoroH the a:ndes oe peeu and bolitia. 263 



type, are here replaced by strongly-folded stratified deposits. The 

 latter consist for the greater part of well-bedded, dark, bituminous 

 limestones weathering to j^ale grey ; but in places they are inter- 

 stratified with beds of an arenaceous character, and Avith black 

 carbonaceous shales containing workable coal-seams. Occasional 

 masses of amygdaloidal lava of contemporaneous origin are also 

 met with. 



It may be recalled that in Southern Peru steeplj^-inclined or 

 inverted beds were found to be the exception rather than the rule, 

 and the folding apparently never reached that degree of intensity 

 which is displaj^ed in the rocks of this district, where vertical dips 

 and overfolds are by no means uncommon. 



In a section of this magnitude, constructed as the result of a 

 somewhat rapid traverse, it has not been thought advisable to 

 attempt more than a diagrammatic representation of the folding, 

 for only by detailed mapping of the district, a task that would 

 take many years to complete, can it be hoped to unravel the correct 

 sequence of the rocks. 



Owing to the nature and intensity of the Tertiary folding, it 

 was not found possible to determine on purely strati graphical 

 grounds the existence of the great break in the succession between 

 Jurassic and Cretaceous rocks which was shown to occur farther 

 south. The two sets of deposits are here almost inextricably 

 welded together in a great folded complex, and all traces of the 

 pre-Cretaceous uplift and subsequent transgressive unconformity 

 have been obliterated by the later folding. A study of the palseon- 

 tological evidence, on the other hand, not only serves to show that 

 the structure of the country is even more intricate than at first 

 sight is apparent, but also furnishes ..strong grounds for supposing 

 that the sequence is in reality not one of unbroken conformity. 



The suggestion, which is so pronounced as almost to amount to 

 a proof, that a great discontinuity is present is afforded by the 

 frequent discovery in close juxtaposition of faunas of Lower 

 Liassic and Middle Cretaceous age ; whereas the beds which should 

 normally intervene appear to be wholly wanting in this district. 

 Further, if this gap in the sequence can be accounted for, as 

 appears probable, on the theory of non-deposition, a ready indication 

 is thus afforded of the source of the littoral leaf-bearing Lower 

 Cretaceous beds of the coastal region. 



Since it would serve no useful purpose to enumerate in detail all 

 tlie localities at which fossils were found, I have confined myself 

 to a generalized description of the three chief faunal horizons 

 represented. 



LIAS. 



Fossils of Liassic age have already been recorded from the 

 provinces of Yauli and Tarma, and the existence of deposits of 

 much wider extent is suggested by the frequent occurrence of 

 derived forms in the morainic drift of the Jauja valley. Along 

 the line of section here described beds containing a characteristic 



