OBJECTIONS TO THE THEORY OF SUBSIDENCE. 297 
d. Examples of massive corals having the top flat, or de- 
pressed and lifeless, while the sides are living, are common 
in coral-reef regions, wherever such corals are exposed to the 
deposition of sediment, and where they have grown up to the 
surface so that the top is bare above low tide. A disk of 
Porites, having the top flat and the sides raised (owing to 
growth) so as to give it an elevated border, is figured on 
Plate LV. of the author’s Report on Zodphytes. Many such 
were found in the impure waters of a shore reef at the 
Feejees. At Tongatabu one flat-topped mass of Porites was 
twenty-five feet in diameter; and both there and in the 
Feejees, others of Astraeids and Mzandrinas measured twelve 
to fifteen feet in diameter. 
Over the dead surfaces, as Mr. Semper observes, the coral 
may be eroded by the solvent action of the waters and espe- 
cially where depressions occur to receive any deposits; and 
and Upolu of the Samoan group, nearly eighteen hundred miles, the drift was only 
forty-three miles. 
The “Challenger,” on her route from the Hawaiian Islands to Tahiti, found, be- 
tween the parallel of 10° S. and Tahiti, “ the general tendency of the current west- 
erly, but its velocity variable; ”” between the parallel of 10° S. and 6° N., the direction 
was westerly with “the average velocity thirty-five miles per day, the range seven- 
teen to seventy miles per day,” the maximum occurring along the parallel of 2° N. 
Farther west, about the Pheenix group, the equatorial current, as described by Mr. 
Hague (loc. cit. p. 237) has “a general direction of west-southwest and a velocity 
sometimes exceeding two miles per hour.” At times it changes suddenly and flows 
as rapidly to the eastward. The drifting of the sands about Baker’s Island (in lati- 
tude 0° 13’ N., longitude 176° 22’ E.) has much interest in connection with this sub- 
ject of current action, and the facts are here cited from Mr. Hague’s.paper. The 
west side of the little island (1 xX 2 m. in area) trends northeast, and the southern 
east by north, and at the junction a spit of sand extends out. During the summer 
the ocean swell, like the wind, comes from the southeast, and strikes the south side; 
and consequently the beach sands of that side are drifted around the point and 
heaped up on the western or leeward side, forming a plateau along the beach two 
or three hundred feet wide, and eight or ten feet deep over the shore platform. 
With October and November comes the winter swell from the northeast, which 
sweeps along the western shore ; and in two or three months the sands of the pla- 
teau are all drifted back to the south side, which is then the protected side, extend- 
ing the beach of that side two or three hundred feet. This lasts until February or 
March when the operation is repeated. 
