132 H. E. Gregory — Geologic Reconnaissance of the 



interrupted drainage speak of a widespread glaciation which 

 has substantially modified the pre-Pleistocene topography. 



The bedrock of the whole region between the Apurimac and 

 Cuzco valleys is brown and grey sandstone, whose continuit}- 

 of stratification is interrupted by lenses of conglomerate and 

 occasional beds of shale. The sandstone strata rarely approach 

 horizontality ; dips of 20°-40° are common, and where expos- 

 ures are favorable these tilted strata are seen in folds open or 

 closed, and with horizontal or steepl} 7 inclined axes. Near the 

 headwaters of the Mollemolle exposures of dense blue-grey 

 limestone, much fractured and in places brecciated, roughen 

 the hill-slopes. This rock, in common with the sandstone, 

 appears to be identical in lithologic character with the strata 

 represented in the Huatanay valley, and the single fossil 

 (Lower Cretaceous) obtained from the limestone is a duplicate 

 of many collected at Cuzco. The Lower Cretaceous limestone 

 overlies strata of sandstone of great extent and more than 1000 

 feet in thickness. The relations existing between the calcare- 

 ous and arenaceous beds have not been determined. Strata 

 containing carbonized plant fragments and unconformably 

 overlying the brown sandstone were found near the village of 

 Paruro, and assigned by Duenas* to the Tertiary. The reasons 

 for such a conclusion are not given, and so far as the writer is 

 aware the only paleontologic evidence of age relations consists 

 of a Lower Cretaceous lamellibranch, and the vertebrate re- 

 mains from Ayusbamba described by Dr. Eaton. 



With the exception of intrusives cutting the Apurimac can- 

 yon wall, no igneous masses were observed, although, as stated 

 below, it is probable that a boss of diorite lies buried beneath 

 the superficial deposits at Ayusbamba. Duenas found that 

 diorite intersected by dikes of red and green labradorite con- 

 taining phenocrysts of augite was associated with the ever- 

 present grey and brown sandstone at several localities in the 

 province of Paruro. 



The discovery of coal in the vicinity of Paruro has from time 

 to time been announced. The basis for such reports is doubt- 

 less the presence of carbonized w T ood and lenses of impure lig- 

 nitic peat which occur among the strata of ancient lake beds. 

 My observations are in accord with the results of a reconnais- 

 sance conducted by Peters and Company, and with the conclu- 

 sion of Duenas, that the quantity of the so-called " coal " is 

 negligible and its quality unsatisfactory. Kock for building, 

 lime for cement, and excellent clay, all of which may be ob- 

 tained in quantity, complete the list of rocks of economic value 

 in the Ayusbamba region. 



*Boletin Cuerpo de Eng. de Min. del Peru, No. 53, 1907, p. 122. 



