Exposed Quaternary Islet Formed By Volcanic Tuff Charles Darwin (1809 – 1882) visited the Galápagos Islands over a 35-day interval in September and October of 1835, during the nearly five-year voyage of the Beagle. He made many original contributions on the geology of the islands in his diary, later drawn on and expanded for publication in his volume on “Geological Observations” (Darwin, 1844). One of the more insightful observations was on the geomorphology of coastal tuff craters with reduced or entirely breeched walls, all examples open to the south. He attributed this phenomenon to the inability of soft tuffaceous rocks to resist wave erosion caused by regional prevailing winds driving ocean swells to the north and northwest. In this photo, looking northeast under the afternoon sun, the steeper inner wall of an eroded crater is seen to the right. The outer gentle slope of the volcano is to the left. More than half of the volcanic islet has been washed away. Also shown is a sea notch and overhang seen in profile to the far right.(Photograph and caption by Dr. Markes E. Johnson, Department of Geosciences, Williams College, Williamstown, Massachusetts, USA).Reference: Darwin, C.R., 1844. Geological Observations on the Volcanic Islands Visited During the Voyage of the H.M.S. Beagle. Smith, Elder & Co., London, 175 p.