Page:The Journal of geology (IA journalofgeology11893univers).pdf/442

The adoption of any general terminology for the pre-Cambrian rocks is deprecated. In the author's judgment, "the term Laurentian cannot henceforth have more than a local significance." He further indicates his belief that "there will be much less impediment to the progress of investigation by the multiplication of local names than by the attempt to force indentifications for which there is no satisfactory basis. Each country will have its own terminology for pre-Cambrian formations, until some way is discovered of correlating these formations in different parts of the globe." The great duration of the time interval represented by the pre-Cambrian sedimentaries and their great unconformities is distinctly recognized. Much fuller details are given in this than in any earlier edition, concerning the development of the pre-Cambrian in different parts of the world. On the whole, the chapter on pre-Cambrian is much more satisfactory than in any other existing text-book. Several other periods are much more fully dealt with in this edition. This is especially true of the Silurian and Tertiary. Various new figures of fossils are introduced, representing important species of recent discovery.

In the section dealing with glacial geology, we notice that no distinction is made between the formations known in America as kames and osars, and are a little surprised to find the statement concerning kames (osars as we know them in America) that "no very satisfactory statement of their mode of origin has yet been given." Perhaps this may be true in a restricted sense, since there is much discussion as to the exact character of the streams which produce them, but that the formations which we have come to call osars were produced chiefly by superglacial or subglacial streams, does not seem to admit of serious question, so far as America is concerned. We are also suprised to find the loess placed in the recent or post-glacial series. This is not the correct reference of most of the loess in the United States, for at various points along the northern border of the very extensive loess covered area, as in Illinois and Iowa, the loess is frequently found beneath the till of the later ice invasions. The eolian theory of the origin of the loess is favored. This seems to be by far the most satisfactory theory for the Asiatic loess, and is finding much favor in connection with the loess of Europe. It is doubtless the loess of these countries to which reference is especially made. But the points urged in support of the eolian theory are not all applicable to the American formation. For example, "the thoroughly oxidized condition" of the iron content of the loess