Composition of certain Mesozoic Igneous Rocks of Virginia
Generally Uniform Composition of Mesozoic Trap. No one has ever studied the earlier Mesozoic formation along the Atlantic border without being struck by the numerous ridges and dikes of trap which are found in connection with it, and no one has ever studied the trap found in these ridges and dikes without being impressed by its uniformity of composition. J. D. Dana* has pointed out the wonderful uniformity of these eruptive rocks, calling them all dolerites; rocks made up essentially of labradorite and pyroxene, with more or less magnetic iron ore in disseminated grains or crystals. He says that the aspect of specimens from Nova Scotia to North Carolina is closely the same, and that the density varies little from 3. The lowest density which he quotes is 2.94, and the highest 3.16. Chemical analyses of these rocks by G. H. Cook,† W. G. Mixter,‡ S. T. . . .