part 3] THROUGH THE AT^'DES OE PERU AND BOLIVIA. 273 



Mexico. Peku. 



Sub- 

 division. 



'Exogyra ponderosa Roemer. 



JExogyra cf. conica Sowerby 

 (large forms). 



Horizon. 





7. 



6. 



Euallaste)' bravoensis Bose. 



Turritella granulata Sowerby, 

 vav. ceuomanensis D'Orbignj'. 



Lima (Mantellum) mexicana 

 Bose. 



PJnallaster peruamis Gabb = 



E. texanus (Roemer). 

 Turritella granulata Sowerby, 



var. ceuomanensis I)'0rbig'n3^ 

 Lima (MantelliimJ cf. mexicana 



Bose. 



Holectgpus planatus Roemer. 

 Pseudodiadema (LiplopodiaJ 



texanum (Roemer). 

 Natica aff. collina Conrad. 

 Pecten cf. chiJiuaJmensis Bose. 

 Pecten (Neitliea) quadricostatus 



Sowerby. 



f3 



5. 



Holectypus limitis Bose. 

 Pseudodiadema (Diplojpodia) 



cf. variolaris Bvongniart. 

 Natica att'. collina Conrad. 

 Pecten chihuahuensis Bose. 

 Vol a quinquecostata Sowerby 



= Pecten qua drico status 



(Sowerby) Roemer. 



4. 



ScMoenha cilia cf. helknapi 

 Marcou. 



Schloenhacliia cf. helknapi 

 (Marcou) Bose. 



Scliloenhacliia multijida Stein- 

 mann. 



Scliloenbachia cf. acutocarinata 



(Sbumard) Bose. 

 Pinna cf. robinaldina D'Orbigny. 

 Tylostoma cf. cliihualmense Bose. 



< 



3- 



Scldoenhachia cf. helknajpi 

 Marcou. 



2. 



ScliloenbacMa afF. acutocarinata 



(Shumard) Marcou. 

 Pinna guadaluptB Bose. 

 Tijlostoma chihualiuense Bose. 



As we commence the descent of the eastern slopes of the 

 Cordillera, we find that this great Mesozoic limestone series extends 

 almost as far as Tarma, where deposits of Liassic age rest upon 

 an older series of conglomerates and quartzites with occasional 

 bands of dolomite, which Prof. Steinmann (relying solely on litho- 

 logical evidence) suggests are of Triassic age. In the absence of 

 fossils, however, it does not at present seem justifiable to separate 

 them definitely from the Jurassic deposits which overlie them 

 conformably. 



From this point to the end of our line of section we have to deal 

 Avith rocks that are of Palseozoic or even earlier age. Relying on 

 the evidence obtained from regions farther south, I regard it as 

 clear that these rocks must have been subjected to several distinct 

 periods of orogenic movement, wdth the result that they have been 

 in many cases highly metamorphosed. 



The structure of the country is thus further complicated, and, in 

 the almost complete absence of fossil remains, the correct sequence 

 of the deposits is by no means easy to determine. Certain apparent 

 anomalies in the succession may be explained either by a S3^stem of 

 thrust-planes along which movement has taken place in an easterlv 



x2 



