1830. ANNIVERSAEY MEMOIES OF THE BOSTON SOCIETY OP NATURAL HISTOEY. 1880. 



PROPOSITIONS CONCERNING 



THE 



CLASSIFICATION OF LAVAS, 



CONSIDERED WITH REFERENCE TO THE CIRCUMSTANCES OF THEIR 



EXTRUSION. 



BY N. S. SHALER. 



BOSTON: 



PUBLISHED BY THE SOCIETY. 



1880. 



