18301830. ANNIVEESAEY lEMOIES OF THE BOSTON SOCIETY OP NATURAL HISTOKY. 1880. 



PROPOSITIONS CONCERNING 



THE 



CLASSIFICATION OF LAVAS, 



CONSIDERED WITH REFERENCE TO THE CIRCUMSTANCES OP THEIR 



EXTRUSION. 



BY N. S. SHALER. 



BOSTON: 



PUBLISHED BY THE SOCIETY. 

 1880. 



