GEOLOGY 1929

by ALFRED C. LANE
Professor of Geology and
Mineralogy, Tufts College

PERHAPS the great achievement of 1929 is the enlistment of more precise physical and chemical methods to help in unraveling the history of the earth and its structure.    For instance, by studying its electric conductivity, more conductive strata have been located perhaps thirty miles down.

Again, the records of the relatively new station for the reception of earthquake waves at Honolulu have identified two or three different layers of rock. Adams and his colleagues of the Geophysical Laboratory have been testing the properties of rocks so that we can tell the velocities with which granites, basalts, etc., propagate such waves, and thus identify the rocks.

Delicate tests of gravitative force have been carried on not only at sea, showing that the sea floor is heavier than the continental rocks, but also in the search for oil. Wells for oil have been carried deeper with startling rapidity. Only a short time ago the deepest well in the United States was 7,756 feet. Now Texas and California are racing with a number of wells over 8,000 and up to 8,600 feet deep.

The age of the upper Cambrian trilobite-bearing shales of Sweden has been estimated by the amount of helium and lead produced from the uranium they contain.  Arthur Holmes has estimated the age of two igneous rocks from the ratio of the helium produced. It seems to me that we may look forward to an approximate dating of geologic strata by the helium ratio within ten years, and that we may look as an ultimate goal to a year-by-year, climatic history of the earth comparable to that which Huntington has worked out from the rings of the California great trees for the last three thousand years. Only this will go back more than three hundred thousand thousand!