70 [ The Silurian rocks occur about the middle of the Primary formations. The eozoön was formerly supposed by some geologists to be a form of fossil. The Laurentian rocks are the lowest strata of the Primary formations.]
71 [ The Jurassic formation occurs about the middle, the Triassic, just below it, in the lower half of the Secondary rocks. The Devonian occurs just above the middle of the Secondary, between the Carboniferous above and the Silurian below.]
72 [ From The Popular Science Monthly, July, 1901.]