40 The American Geologist. jniy, \mi 
Whatever the origin of the upper hxterite of India (see above), 
the lower laterite has un(loul)tedly been derived fro;ii it in large 
measure by stream action. The most reasonable explanation of 
the change of conditions from a residual soil producing region (if 
this explanation be accepted for the upper laterite) to a region of 
denudation is that of elevation and consequently the giving of 
new powers to the streams. The lower laterite occurs generally 
near the shore and apparently extends out to sea beyond the pres- 
ent shore line. Its thickness is seldom greater than fifty feet, it 
is always sandy and sometimes contains rounded pebbles. Human 
implements found with the deposit prove it to be of recent origin. 
Medlicolt and Blanford* believe it to have been subaerially de- 
rived from the upper laterite. In part, if not entirely, it has been 
formed Iteneath the sea having been transported tliither by river 
action, and having been raised to its present position by a recent 
elevation. 
The importance of these suggestions in the explanation of cer- 
tain geological phenomena of the past may be very great. In the 
Carboniferous, for instance, numerous recurrent elevations and 
depi'essions are recorded and with them great quantities of sedi- 
ment were derived and deposited. In many regions great beds of 
clay were laid down, often having such a character as to admit of 
the explanation of residual origin. The remarkable development 
of lilue, yellow, red aild mottled clays in the Central Texas 
Carboniferoust may possibly be explained in this way. These 
deposits are often quite barren of fossils, indicating a very 
muddy sea. 
The Carboniferous time was one well adapted to the accumula- 
tion of a residual soil, being apparently one of considerable moist- 
ure, much vegetation, general warmth, and of low lying lands. 
The elevations and depressions so well recorded must have furn- 
ished the means of removal of any such soils, either by the 
actual encroachment of the sea, or by the erosion of the land 
by subaerial agents, or by both. Such an explanation makes it 
easier to understand the extensive accumulations of cla3's in these 
deposits. Similar deposits in other ages may have had a similar 
origin. On this subject Pumpelly writest "the very fine marine 
-•- 
^Geology of India, Vol. i. 
tTarr. First Ann. Rept. Texas Geol. Survey, 209-212. 
JAm. J. Sci., 1879, xvir, 133-144. 
