GEOL. VOL. I.] SMITH SANTA CAT A LIN A ISLAND. 69 



have been sufficient to form two islands of the mass, the 

 channel between them extending from a little to the west of 

 the isthmus, three or four miles to the east. This is based 

 on the fact that between these points the main ridge falls 

 considerably below the 1,400 ft. level. It may be, however, 

 that this decrease in altitude is a part of the local depression 

 hereafter suggested in connection with the isthmus. 



The submergence was followed by a long period of ero- 

 sion, during which the then existing island (or islands) was 

 reduced to the peneplain condition. The main body was a 

 low and nearly level area, above which, near the center, 

 projected the higher andesitic peaks. This area contained 

 a bay of considerable size, occupying the Little Harbor 

 region. The reduction of the island to a peneplain was 

 followed by an elevation, the amount of which is approxi- 

 mately indicated by the 350 feet submarine contour, thus 

 making the altitude of the peneplain, roughly, 1,850 

 feet. This movement was gradual, and was interrupted 

 by at least one pause, at an elevation of 600 or 700 feet 

 above the present sea-level. This is shown by the levelled 

 slopes in the lower portion of the Little Harbor region, and 

 by the sedimentary deposits found on these slopes. The 

 island remained at its highest level long enough to carve the 

 broad submarine bench on the most exposed side. A very 

 slow subsidence may have taken place at this time. It was 

 followed by the present period of comparatively rapid sink- 

 ing. 



This most recent period has been a short one, as is shown 

 by the small amount of cliff cutting, which has taken place 

 since it began, on those parts of the island most exposed to 

 wave action. It was during the period of rapid submergence 

 that the stream valleys of the present drainage system were 

 flooded in their lower portions (see Plate III, fig. i, and 

 fig. i, page 4). For while the broad submarine platform 

 was being carved about the island, whatever subsidence 

 there may have been was not too rapid for the cliff cutting 

 easily to keep pace with it. Thus no valley drowning could 

 take place, and no trace of buried channels or sunken 



