1883.] Geological Effects of a Varying Rotation of the Earth. 21 
coral islands. His map has been often copied. From this, and 
the statements of numerous recent observers, we may establish 
the following generalizations : 
I. Areas closely adjacent to active volcanoes, with very few 
exceptions, are rising. For example, Sunda islands, Sandwich 
islands, Philippines, West Indies, Central America, etc. 
2. Extensive alluvial, and marine plains, rapidly formed, seem 
frequently to be areas of subsidence. For exdmple, deltas of 
the Po, Indus, Ganges and Mississippi, Holland (?), New Jersey (?), 
North Carolina (?). 
3. All islands, not volcanic, between the parallels of 30° lati- 
tude, bear signs of recent sinking; except Ceylon, of which some, 
however, report evidences of sinking, and Madagascar, which 
shows evidence of recent extinction of volcanic action. 
4. The continents, within the same boundaries, not infrequently 
show signs of sinking. The Great Barrier reef testifies to the 
sinking of Northern Australia. From tropical Africa little is re- 
ported which bears upon our case. 
South America is reported as sinking at the mouth of the 
Amazon, by Agassiz; as being bordered with barrier coral reefs, 
‘from Abrolhos islands to the equator, by C. F. Hartt. A sunken 
sandstone reef at Pernambuco, underneath the present one, is re- 
ported by J. C. Hawkshaw. Demerara is protected by dikes from 
the encroaching sea (F. M. Endlich). Upon the west side of the 
continent, although it may be considered a volcanic area, Von 
Tschudi reports a subsidence of the coast, at Peru, since its dis- 
covery. Bousingault, Proctor and Orton consider that there is 
strong evidence that the Peruvian and Columbian Andes have 
sunk considerably since the visit of Humboldt. Darwin reports 
-a depression of Callao, by the earthquake of 1746. 
Some exceptions should be noted under this head. Texas is 
reported to be rapidly rising. This may be due to its nearness to 
the probably rising axis of the Rocky mountains, which en- 
roaches upon the tropical area. India seems to be S at 
several points, as at Bombay, Sinde, Orissa, &c. 
5. Areas outside of about 30° latitude are very generally rising. 
Avoiding, for the present, those near volcanoes, we enumerate: 
In the northern hemisphere: Scandinavia, Scotland, France, 
Spain, North Africa (Reclus), Russia (Murchison), Spitzbergen 
(Lamont), Franz-Joseph-Land (Howorth), Siberia (Wrangell), 
