PLATE XVII. 



The difference in level between Plnte XI and Plate XII is too .crreat to permit 

 of a satisfactory study of the changes in form of the flocculi at different heif^hts 

 above the i)h()tosi>here. In the ])resent series it is fortunattdy possible to ,s;ive 

 an intermediate ste]). olitained Iiy settin.i; the s(M-ond slit immediately outside of 

 H, : the level shown therefore lies between that of Plate X\' and that of Plate 



xViii. 



PLATE XVIII. 



This i)hotograph is jjiven here in the endeavor to bring out the bright 

 eruptive tongues, hardly to be distinguished from the less brilliant flocculi. 

 The abnormally dark background necessarily results from the deep printing 

 reciuired to show the exceedingly brilliant details. 



162 



