EXPLANATION OF PLATE IV 
The figures are from drawings of thin rock sections as seen under 
the microscope. 
Upper Figure. — Andesite 
Compact lava from the east base of the Bogoslof Volcano, Bering 
Sea, collected in 1899. This volcano first appeared above the sea in 
May, 1796, l^eing thrown up close to Ship Rock, a perishing remnant 
of an earlier volcano. It is sometimes called Old Bogoslof, to distin¬ 
guish it from New Bogoslof, the eruption of which began in 1883. 
The history of the volcanoes is given in volume 11, pages 291-335. 
The rock is described on page 30 of this volume. Drawn with 
natural light, but with nicols crossed to bring out the zonal structure 
of the plagioclase. Magnified 28 times. 
Lower Figure. — Liparite 
The specimen was collected as a rolled boulder from a beach on the 
north side of St. Lawrence Island, Bering Sea. See pages 38 and 41. 
Drawn with natural light. Magnified 28 times. 
