INTRODUCTION 497 



the creeks. They are composed generally of luistratified clays, sands, 

 gravels, and boulders. The latter, 10 pounds to several tons in weight, 

 are usually angular and subangular and composed generally of aurifer- 

 ous quartz, granites, syenites, and other hornblendic and feldspathic 

 rocks. The ridges have been greatly eroded and the boulders exposed. 

 To my keen regret, my travels did not quite extend to this intensely 

 interesting "glaciated" region. 



Courtenay De Kalb visited the Siempre A^iva mine in the Pis-Pis 

 district and says :^ 



"The geology of the region is very simple. Along the eastern flanks of the 

 mountains occur carboniferous limestones, npon which lie unconformably red 

 sandstones and variegated shales evidently belonging to the Permian period. 

 Basaltic dykes have obtruded through these rocks at many places, and higher 

 up all traces of the Permian formations are lost sight of, the mountain masses 

 being composed entirely of rocks of the dioritic group, largely porphyritic, and 

 of metamorphosed shales. It is along the lines of contact between diorites 

 and shales that the veins are found." 



C. Willard Hayes, as the result of a study^ of the "Nicaraguan depres- 

 sion,^' thinks that in early Tertiary times the Atlantic and Pacific were 

 united across Nicaragua; that the country was elevated in mid-Tertiary 

 times, and this was followed by a long period of erosion which developed 

 a broad peneplain, above which are residual hills, most abundant at the 

 axis of the isthmus, where the continental divide was formerly located, 

 but merging northward with the mountains of northern jSTicaragua ; 

 that another elevation (of 200 or 300 feet) resulted in the erosion of 

 valleys beneath the peneplain, and that the latest episode has been a de- 

 pression of 100 or 200 feet that has drowned the lower portions of the 

 river valleys, and the drowned portion has been largely silted up. 



W. A. Connelly has described^ the country rock of the Pis-Pis district 

 as "a flow or succession of flows of andesite, much fractured and highly 

 altered near the surface," and T. Lane Carter says^ that it is generally 

 porphyry. 



Quaternary Deposits 



detailed descriptions 



The Wanks Eiver enters the Caribbean Sea at the end of the promi- 

 nent headland known as Cape Gracias a Dios. The headland consists 



5 The new gold fields of the ^losquito coast of XicaraRiia. Eng. and Min. Jour., vol. 

 Ivii, pp. 294-295. 



« Physiography of Nicaragua Canal route. Nat. Geog. Mag., vol. x, 1800, pp. 233-246. 



■^Pis-Pis district, Nicaragua. Min. and Sci. Press, vol. 100, No. 10, March .">. 1010, 

 pp. 350-351. 



8 Mining In Nicaragua. Bull. Amer. Inst. Min. Eng., No. 4S, December, 1910, pp. 

 965-1001. 



