_Table of Specific Gravities of Trachytes of the Henry Mountains._ ───────────────────────────────────────────────────┬───────────────── Locality. │Specific gravity. ───────────────────────────────────────────────────┼───────────────── East flank of Mount Pennell; sheet │ 2.66 Marvine Laccolite; north base of Mount Ellen │ 2.65 Peale Laccolite; east flank of Mount Ellen │ 2.64 Dike on Mount Ellsworth │ 2.64 South base of Mount Hillers; sheet │ 2.63 Sheet under the Peale Laccolite │ 2.62 Scrope Laccolite; southeast base of Mount Ellen │ 2.60 Bowl Creek Laccolite; northeast base of Mount Ellen│ 2.58 North spur of Mount Pennell; dike │ 2.58 Sentinel Laccolite; north base of Mount Pennell │ 2.54 │ ———— Mean │ 2.61 ───────────────────────────────────────────────────┴───────────────── Specimens to represent the stratigraphic series were selected at the _margins_ of the disturbed region so far as possible, to avoid the effect of metamorphism. But as it was not practicable to eliminate this source of error in every case, the densities of highly metamorphic specimens were also measured for the purpose of indicating the effect of the metamorphism. In order to restore so far as practicable the condition of the rocks at the time of the lavic intrusion, the specimens were saturated with water, and in this condition were weighed in air as well as in water. The results for the porous sandstones are from one-seventh to one-fourteenth lower than would have been obtained by the usual method. Hand specimens were used as before.