258 ME. J. A. DOUGLAS 01^ GEOLOGICAL SECTIONS [vol. Ixxvii, 



conglomerate of the Cretaceous in the south, and if we are to regard 

 an intrusion of this nature as the accompaniment of orographic 

 movement it is not unreasonable to suppose that this phase took 

 place during the post-Jurassic pre-Cretaceous folding. 



Moreover, although prior to the intrusion of the second or 

 dioritic phase the earlier rocks were evidently subjected to intense 

 crushing, and in man}' cases were converted into true banded 

 gneisses, it was shown that the interval of time which elapsed 

 between the intrusion of the first and that of the second phase 

 could not even approximately be conjectured. 



If now, however, we apply the evidence gained from the district 

 here described that the second and third phases are post- Cretaceous, 

 and probably took place during the great Tertiary uplift of the 

 Andes, it will be seen that this interval must have comprised the 

 whole of the Cretaceous and early Tertiary periods ; and we can 

 regard the gneissic structure, which is not shared by the later rocks, 

 as having been produced in those already in existence as a dynamic 

 effect of this uplift. 



Prof. Lisson ^ has given a detailed microscopic description of the 

 granodiorites and diorites of the Lima district, and it is onh^ 

 necessary to add that they appear to be essential Iv similar to those 

 which I have formerl}^ described from Southern Peru. 



When the eastern limit of the zone of plutonic rocks is reached 

 near Matucana, the above-described normal facies of shallow- water 

 Cretaceous deposits is found to have given place to the second or 

 volcanic facies, consisting largely of bedded tuffs and agglomerates; 

 a type of deposit that has a wide distribution in the Western 

 Cordillera of Southern Peru. 



These beds are strongly folded, and although they are occasion- 

 ally interbedded with limestones and quartzites, in the absence of 

 paleeontological evidence from the latter it is impossible, without 

 reference to other districts, to assign them definitely to any one 

 geological period. Volcanic activity is known to have already been 

 rife in Southern Peru in Jurassic times, and Forbes regarded the 

 ' porphyritic conglomerate ' of Bolivia as having also been formed 

 during this epoch. 



In my experience, however, with the exception of isolated 

 occurrences such as the pillow-lava of the Morro de Arica, inter- 

 bedded volcanic rocks are not as a rule found in the normal 

 Jurassic sediments of the south, and they are also absent from the 

 fossiliferous Jurassic rocks encountered in the district now de- 

 scribed. Furthermore, it has been shown that volcanic rocks, 

 except in the form of subsequent intrusions, are but seldom met 

 with in the Lower Cretaceous Series of the Lima district. In later 

 Cretaceous deposits, however, they are of widespread occurrence. 



During the course of a further traverse, from Pacasmayo to 

 Cajamarca, on the western slopes of the Cordillera ISTegra, thick 

 beds of tuff and agglomerate together with lava-flows were found 



^ ' Geologia de Lima & sus Alrededores ' 1907, pp. 95-106. 



