part 3] THEOUGH THE ANDES OF PERU AND BOLIVIA. 277 



In the immediate iieighbourliood of Lima we encounter the 

 great Tertiary batholithic core of granodiorite, cutting sharply 

 across the dip of these Cretaceous rocks and causing pronounced 

 metamorphism along the margin of contact. From this point 

 plutonic rocks crop out almost continuously as far as Matucana. 

 The intrusion appears to have taken place in two distinct phases : 

 the first represented by a diorite, the second by a more acid grano- 

 diorite ; and these are compared with the corresponding phases 

 formerly described from the rocks of the Cerros de la Caldera, 

 near Arequipa. 



Beyond Matucana we meet with the second of the three distinct 

 types of deposit exhibited b}^ the Mesozoic rocks of Central Peru. 

 This is the so-called ' volcanic facies,' and consists chiefly of beds 

 of porphyritic agglomerate, though in places these are associated 

 with more normal types of deposit such as limestones and quartzites. 

 It is almost entirely confined to the western slopes of the Cordillera, 

 and in view of the evidence obtained in the district of Cajamarca, 

 farther north, its age is thought to be not earlier than the Ceno- 

 manian. 



Later intrusions of andesite and dacite, probably of Tertiary 

 age, are also of common occurrence in this district, though all 

 trace of recent volcanic activit}^ is Avanting. 



The underlying granodiorite core, although not actually exposed 

 at this altitude along the line of section, must be very near the 

 surface, for it comes to light close at hand in the Morococha 

 Valley, where it is associated with a large laccolitic intrusion of 

 dacite. Its outcrop is here nearly 16,000 feet above sea-level, and 

 it thus plays a very important part in the construction of the 

 Cordillera. 



After crossing the summit of the range near Ticlio, we encounter 

 a third zone of Mesozoic rocks, consisting for the greater part of 

 limestones, in manj^ places richl}^ fossiliferous. The beds are 

 everywhere strongly folded, and frequently show vertical and 

 reversed dips. Palseontological evidence tends to indicate the 

 presence of a great break in the geological sequence, beds of 

 Liassic age being found in close proximit}^ to those containing a 

 fauna characteristic of the Albian, while de^oosits that should 

 normally intervene appear to be entirely w^anting. These fossili- 

 ferous limestones probably extend into the Cenomanian, but no 

 evidence was obtained of the existence in the district of beds of 

 later age than this. 



Mesozoic rocks are continued down the eastern slopes of the 

 Cordillera as far as Tarma, where they rest unconformably on 

 strongly-folded rocks of Palaeozoic age. Owing to the almost 

 complete absence of fossils in the latter, however, it is impossible 

 for the present to assign them to any definite geological formation. 

 Limestones thought to be of Carboniferous age are found near 

 Palca and again below Utcuyacu ; but, for the greater part, the 

 rocks consist of metamorphosed phyllites and mica-schists pene- 

 trated by a granite which has also shared in the dynamic crushing 



