82 TAYLOR'S GEOLOGICAL RECONNOISSANCE. 



The writer has endeavored to illustrate the topography of the Palenque and 

 Escribanos district, by a map and coast sketch, which are appended to this article. 



This map, (Plate X, fig. 1,) is simply the result of a preliminary reconnoissance ; 

 and is constructed from data hastily acquired, and is wholly unassisted by 

 previously existing maps or charts. It must be borne in mind, that the natural 

 difficulties inseparable from such a climate ; from a surface unusually broken and 

 intersected by a labyrinth of ravines; from the extraordinary denseness of its 

 magnificent vegetation ; from the deluges of almost daily rains, and from the total 

 absence of all roads and paths, offer serious obstacles to the scientific explorer. It is 

 scarcely probable that any description of survey, whether geological or topographical, 

 has ever before been attempted, in this quarter. 



Fig. 2, is a coast sketch of the interior, looking south from the anchorage, off 

 Escribanos. It is a highly interesting region, and is characteristic of the aspect and 

 geological structure of this part of the Isthmus. The geologist cannot fail to recognise, 

 in the serrated outline of the distant Calohre mountains, the igneous character of the 

 group which occupies the centre of the Isthmus. The auriferous zone, including 

 the mines of San Antonio, occupies the intermediate space between the Calobre 

 mountain chain and the Caribbean sea. 



Geological Memoranda. 



Throughout the small district which it is the design of this paper to illustrate, the 

 prevailing rock formation is of the porphyritic class. It is moreover distinguished 

 by the numerous quartz veins or parallel seams, which are charged with gold. 

 These quartz veins are commonly inclosed in thick bands of clay, which may 

 possibly owe their present appearance to disintegration of argillaceous rocks. 



Intermingled with this series occur several varieties of porphyroid, pyritous, 

 ferruginous, and granitoid trap ; associated also with the flint slate, Lydian stone, or 

 touch-stone of the goldsmiths. All of these rocks are more or less decomposed on 

 their surfaces, or at their almost vertical outcrops. 



The variety of porph}/ ry which encloses gold does not appear to extend more than 

 about thirty miles from Escribanos in the direction of Chagres, and Panama. 

 Consequently, this circumstance has in some degree prevented the attention of the 

 thousands of adventurers, who have hurried across the Isthmus to seek the El Dorado 

 of California, from being diverted to other points of mineral value. 



The rock upon which the magnificent old castle of Chagres stands, consists of a 

 decomposing porphyry, whose component particles, after exposure to the atmosphere, 

 lose their cohesion and crumble to pieces. This rock overlies thick beds of trap, 

 which, as seen from the anchorage, are apparently horizontal. Similar beds are 

 observable in the cliff at the mouth of the Rio Palenque of our sketch. 



