IV CONTENTS. 
PAGE 
Romal vesuvose [leucitite] 121 
Galeral albanose-jugose [leucitite] 123 
Fiordinal fiasconose [leucite-basanite] 126 
Romal albanose [leucitite] 130 
Saccal albanose [leucitite] 133 
Boval albanose [melilitic leucitite, cecilite] 138 
Correlation of types 141 
Petrology 144 
Geologic occurrence 144 
Chemical characters 145 
Normative characters 151 
Relations of norm and mode 154 
Mineralogical characters 155 
Soda-orthoclase 156 
Soda-lime feldspar 156 
Leucite 157 
Nephelite 157 
Sodalite and haiiyne 157 
Augite 157 
Hypersthene 158 
Biotite 158 
Olivine 158 
Melilite 159 
Absence of minerals 159 
Textural characters 159 
Space relations 160 
Vulsinian District 161 
Ciminian District 162 
Sabatinian District 163 
Latian District 164 
Hernican District 164 
Auruncan District 164 
Campanian District 165 
Distribution of magmas 166 
Progression of types 169 
The rocks of the Tuscan Region 170 
Quantitative relations 170 
Quantitative relations of the magmas 172 
The average magma 173 
Time relations 175 
Geologic age of the eruptions 175 
Order of succession of the types 176 
Comparison with other regions 177 
The formation of leucite 181 
The Roman Region 181 
Conclusions 185 
The distribution of barium 188 
Bibliography 192 
Index 195 
