—, 
No. 13. — Reports on the Dredging Operations off the West Coast of 
Central America to the Galapagos, to the West Coast of Mexico, 
and in the Gulf of California, in charge of ALEXANDER AGASSIZ, 
carried on by the U. S. Fish Commission Steamer “ Albatross,” 
Lieut. Commander Z. L. TANNER, U. S. N., Commanding. 
[Published by permission of Marsuaty McDonatp, U. S. Fish Commissioner. ] 
Vv. 
Report upon Rocks collected from the Galapagos Islands. By Grorce P. 
MERRILL. 
So far. as the present writer is aware, the volcanic rocks of the 
Galapagos Islands have been the subject of but little investigation. 
Darwin in his “ Voyage of the Beagle” (pp. 372 et seq.) describes the 
islands as volcanic, and the character of the material as black basaltic 
lava with scoria and tuffs. Naturally, his studies did not at that time 
include an examination of thin sections under the microscope. A more 
detailed description of the rocks of these islands is given by Dr. F. A. 
Gooch, in Tschermak’s “ Mineralogische Mittheilungen’’ for 1876 (pp. 133 
et seq.). According to the latter, the volcanic materials examined by 
him are all of a basaltic character, and in part closely correspond to 
those at present under consideration. Dr. Gooch’s specimens were how- 
ever from the islands of Bindloe, Abington, Hood, and Charles, none 
of which localities are represented in the series received from the Fish 
Commission. 
A reference to this paper is however of importance. How well the 
speicmens now examined represent the sources from which they were 
taken, the present writer has no means of deciding. It is assumed that 
they are fairly typical. 
VOL. XVI. — No. 13. 
