h Observations on the
Structure and Growth of Volcanic Cones." "Proc. Geol. Soc." Volume VI.,
1850, pages 207-34. In a letter to Bunbury (January 17th, 1850)
Lyell wrote:..."Darwin adopts my views as to Mauritius, St. Jago, and
so-called elevation craters, which he has examined, and was puzzled
with."--"Life of Sir Charles Lyell," Volume II., page 158.)

Please tell Sir C. Lyell that outside the crater-like mountains at St.
Jago, even throughout a distance of two or three miles, there has been
much denudation of the older volcanic rocks contemporaneous with those
of the ring of mountains. (484/2. The island of St. Jago, one of the
Cape de Verde group, is fully described in the "Volcanic Islands,"
Chapter 1.)

I hope that you will not find the page troublesome, and that you will
forgive me asking you.

LETTER 485. TO C. LYELL. [November 6th, 1849].

I have been deeply interested in your letter, and so far, at least,
worthy of the time it must have cost you to write it. I have not much to
say. I look at the whole question as settled. Santorin is splendid!
it is conclusive! it is perfect! (485/1. "The Gulf of Santorin, in the
Grecian Archipelago, has been for two thousand years a scene of active
volcanic operations. The largest of the three outer islands of the
groups (to which the general name of Santorin is given) is called Thera
(or sometimes Santorin), and forms more than two-thirds of the circuit
of the Gulf" ("Principles of Geology," Volume II., Edition X., London,
1868, page 65). Lyell attributed "the moderate slope of the beds in
Thera...to their having originally descended the inclined flanks of a
large volcanic cone..."; he refuted the theory of "Elevation Craters" by
Leopold von Buch, which explained the slope of the rocks in a volcanic
mountain by assuming that the inclined beds had been originally
horizontal and subsequently tilted by an explosion.) You have read
Dufrenoy in a hurry, I think, and added to the difficulty--it is
the whole hill or "colline" which is composed of tuff with
cross-stratification; the central boss or "monticule" is simply
trachyte. Now, I have described one tuff crater at Galapagos (page 108)
(485/2. The pages refer to Darwin's "Geological Observations on the
Volcanic Islands, etc." 1844.) which has broken through a great solid
sheet of basalt: why should not an irregular mass of trachyte have
been left in the middle after the explosion and emission of mud which
produced the ov