424 Reviews — Bertrand 8f Zurcher — Central American Geology. 



a poor time of it, and he reminds bis readers that during the earth- 

 quake of May, 1844, the waters of Lake Nicaragua rose and caused 

 tremendous damage along its shores. Hence he issues a warning 

 against the folly of entering into a hopeless contest with the forces 

 of Nature. 



Reverting once more to the Isthmus of Panama, Professor Bertrand 

 points out that in the whole of the region included between Chiriqui, 

 whose last eruption was in the sixteenth century, and Tolima, the 

 most northern volcano of the Andean system, there are no recent 

 volcanoes : it is a region of calm between the two Americas. As 

 we have already seen, the latest eruptions date from the end of the 

 Miocene period. The lowering of the platform at Panama is due, 

 not to a transverse fracture, but to a lesser manifestation of the 

 forces which have caused the Isthmus to rise up. " The Isthmus," 

 he says, " is formed by an extremely flattened vault, showing in 

 the centre flows and breccias of Oligocene age, on which repose 

 on either side, with a slight inclination, the series of Aquitanian and 

 Miocene beds. The eruptions, for the most part submarine, have 

 continued intermittently to the end of the Miocene ; then came the 

 uplift, before the Pliocene, which has formed the central anticlinal 

 of the Isthmus. This anticlinal is most conspicuous from north-west 

 to south-east, consequently it has made its mark more strongly in 

 the contour of the country." This is the sole cause of the natural 

 gap of Panama. He further entertains the question of earthquakes 

 in this district, which, when compared with those of other places 

 in Central America, seem to be unimportant. The question of the 

 subsidence of the Bay of Panama is discussed in connection with the 

 hypothesis of Suess of a progressive subsidence of the Pacifi.o coast. 

 He concludes that there really has been a subsidence, so far as the 

 Bay of Panama is concerned, but he does not see any indication 

 that the phenomenon is likely to continue. 



The concluding part of this memoir deals with the great structural 

 lines of Central America and of the Caribbean Sea, including also 

 the adjacent portion of the South American continent. In this 

 the author to a certain extent reflects the views of Suess. It is 

 a question of high tectonics, which has only an indirect bearing 

 on the comparative merits of the Panama and Nicaragua routes. 

 The author supplies his readers with a very useful sketch-map, 

 a perusal of which will enable them to follow his views. The 

 main conclusion with which we are concerned is the establishment 

 of a hypothetical line which he calls an arete de rebroussement. 

 This, he says, is the true line of division between North America, 

 including the Caribbean Sea, and South America ; its results, as 

 regards volcanoes and earthquakes, have the effect of producing 

 a region of calms, a sort of dead angle, where Panama has the 

 good fortune to be situated at about an equal distance from two 

 dangerous lines. 



The following are his conclusions : — 



There are no volcanoes around Panama, all eruption having ceased 

 Bince the Miocene : this is the first point and the most important of all. 



