Sir IT. H. Hoivorth — Surface Geology of N. Europe. 195 



by two coastal plains. The high plateau of Mexico, with levels up to 

 10,000 feet, here descends for a distance of 60 to 80 miles, to levels 

 of '1,000 to 4,000 feet, and at the divide is (as already stated) only, 

 about 1,000 feet above the level of the ocean ; but on both sides of the^ 

 saddle there are base-levels of lower altitudes. The rock consists of 

 earthy sandstone ; and on the Pacific slope facing the city of Tehuan- 

 tepec are old sea-cliiFs and caves at levels of. 400 feet. The floor of 

 the divide is traversed by a " geological canal," atalevelof 776 feet 

 above the ocean, and is covered by gravel, from 4 to 8 feet in 

 depth, of quartz and soft sandstone pebbles, the latter being well 

 rounded; this gravel is more thinly scattered over the adjoining 

 slopes to a height of 150 feet. The isthmus was evidently: swept 

 over by ocean-currents passing through the straits during sub- 

 mergence; and its elevation has been so recent that only short 

 canons have been cut into the base-levels and terraced plains 

 adjoining. Another line of communication was recognized at the 

 pass of Tarifa, a dozen miles eastward of that of Chivela above 

 described ; and there are other current-swept depressions in this 

 region through which the waters on both sides are considered to 

 have had intercommunication, though at higher levels. It' should 

 be added that the stratified gravelof the divide is continuous with 

 that covering the terraced plains on the Gulf side of the divide. ; 

 The author considers that this oceanic connection was as old as 

 the Columbian (Mid-Pleistocene) epoch, and was contemporaneous 

 with the great emergence of the Antillean Continent and Eastern 

 America. It is a splendid illustration of the Lyellian doctrine of 

 ■the interchange of land and sea, which geological phenomena bear 

 testimony to from early, down to recent, times, and which serves as 

 &■ key to many problems in terrestrial physics. Finally, it must not 

 be forgotten that the biological evidence of the former oceanic com- 

 munication across the Isthmus of Panama is not less clear than is 

 the physical. The late Dr. W. B. Carpenter identified 35. species 

 of molluscs, out of 1,400 Pacific forms, as occurring on the Atlantic 

 side of this region; the number having been since increased to 

 100 species, by the observation of Mr. Charles T. Simpson ;; while, 

 according to the late Dr. G. B. Goode, there is absolutely : no 

 resemblance between the deep-water fishes on the two sides of 

 Central America. 



II. — The Surface Geology of the Nokthof Europe, as illus- 



. 



TRATED BY THE ASAR OR OSAR OF SoANDINAVIA AND EiNLAND. 



By Sir Henky H. Howorth, K.C.I.E., M.P., F.E.S., F.G.S. 



PLATE VII. 



IN a previous paper I ventured to eniphasize the opinion, now very 

 generally held, that, whether by , a; gradual, process or spas- 

 modically, the Northern and Central parts of Scandinavia, have been 

 rising from the sea-level since Tertiary times, and that, so far as we 

 know, this rise has not been interrupted by intervals when the 

 movement has been one of depression. The movement has, in fact. 



