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, being 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 n, pages 29133=5. 

 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. 



