August 25th, 1860, page 256; September 15th, page
355; September 29th, page 415; October 13th, page 483. Also letter from
J. Beete Jukes, Local Director of the Geological Survey of Ireland, loc.
cit., September 8th, page 322; October 6th, page 451.), by Sir H. James
(though his letter seemed to me mighty poor, and what Jukes wrote good),
reminded me of this notion. In case astronomical agencies should ever
be proved or rendered probable, I imagine, as in nutation or precession,
that an upward movement or protrusion of fluidified matter below might
be immediately followed by movement of an opposite nature. This is all
that I meant.

I have not read Jamieson, or yet got the number. (492/2. Possibly
William Jameson, "Journey from Quito to Cayambe," "Geog. Soc. Journ."
Volume XXXI., page 184, 1861.) I was very much struck with Forbes'
explanation of n[itrate] of soda beds and the saliferous crust, which
I saw and examined at Iquique. (492/3. "On the Geology of Bolivia and
Southern Peru," by D. Forbes, "Quart. Journ. Geol. Soc." Volume XVII.,
page 7, 1861. Mr. Forbes attributes the formation of the saline deposits
to lagoons of salt water, the communication of which with the sea has
been cut off by the rising of the land (loc. cit., page 13).) I often
speculated on the greater rise inland of the Cordilleras, and could
never satisfy myself...

I have not read Stur, and am awfully behindhand in many things...(492/4.
The end of this letter is published as a footnote in "Life and Letters,"
II., page 352.)

(FIGURE 5. Map of part of South America and the Galapagos Archipelago.)

LETTER 493. TO C. LYELL. Down, July 18th [1867].

(493/1. The first part of this letter is published in "Life and
Letters," III., page 71.)

(493/2. Tahiti (Society Islands) is coloured blue in the map showing
the distribution of the different kinds of reefs in "The Structure and
Distribution of Coral Reefs," Edition III., 1889, page 185. The blue
colour indicates the existence of barrier reefs and atolls which, on
Darwin's theory, point to subsidence.)

Tahiti is, I believe, rightly coloured, for the reefs are so far from
the land, and the ocean so deep, that there must have been subsidence,
though not very recently. I looked carefully, and there is no evidence
of recent elevation. I quite agree with you versus Herschel on Volcanic
Islands. (493/3. Sir John Herschel suggested that the accumulation on
the sea-floor of sediment, derived from t