322 PLATEAU OP CAXAMARCA. 



miles), from the coast of the Pacific on the east of Panama. 

 On the Pacific side the isthmus is almost equally indented 

 by the deep Golfo de San Miguel, into which the Rio 

 Tuyra falls, with its tributary river the Chuchunque (Chu- 

 chunaque). This last-named stream in the upper part of 

 its course approaches within 16 English geographical miles 

 of the Atlantic side of the isthmus to the west of Cape 

 Tiburon. For more than twenty years I have had inquiries 

 made from me on the subject of the problem of the Isthmus 

 of Panama, by associations desirous of employing conside- 

 rable pecuniary means : but the simple advice which I have 

 given has never been followed. Every scientifically educated 

 engineer knows that between the tropics, (even without 

 corresponding observations), good barometric measurements 

 (the horary variations being taken into account) afford 

 results which are well assured to less than from 70 to 90 

 French or 75 to 96 English feet. It would besides be 

 easy to establish for a few months on the two shores two fixed 

 corresponding barometric stations, and to compare repeatedly 

 the portable instruments employed in preliminary levelling, 

 with each other and with those at the fixed stations. Let 

 that part be particularly examined where, near the continent 

 of South America, the separating mountain ridge sinks into 

 hills. Seeing the importance of the subject to the great 

 commerce of the world, the research ought not, as hi- 

 therto, to be restricted to a limited field. A great and com- 

 prehensive work, which shall include the whole eastern part 

 of the Isthmus, and which will be equally useful for every 

 possible kind of operation or construction, for canal, or for 



