Page:The Journal of geology (IA journalofgeology21894univers).pdf/451

This brochure almost opens a new chapter in geological history; for although the formation is essentially a surface feature over an area of 100,000 square miles, and only thinly-covered by a mantle of Columbia sands extending over another 150,000 miles, yet the knowledge of these deposits was fragmentary, and they were not correlated as a unit or interpreted in their bearing on the physical history of the continent, until the appearance of this work.^[1] The investigation of the formation was commenced in Mississippi by Professor E. W. Hilgard, who gave it the above name, though the later appellation of "Orange Sand," given by Professor J. M. Safford, in Tennessee, was commonly accepted. Subsequently, McGee's researches along the Atlantic border made known the Appomattox formation, which the author afterwards found to be a northern continuation of Hilgard's Lafayette, or the "Orange Sand." Confusion also arose in the application of the latter name, and by consent of all the authors, Hilgard's original name was adopted.

The report is written in a narrative form in only a few chapters, which are unfortunately not sufficiently subdivided under topical headings to make the arrangement most favorable as a work of reference. On the other hand, the set of maps is particularly clear and explanatory of the text.

"The Lafayette formation may briefly be described as an extensive sheet of loams, clays, and sands of prevailing orange hues, generally massive above, generally stratified below, with local accumulations of gravel along the water-ways", (p. 489). The physical structure is peculiar, although the deposit resembles certain residuary clays derived from the Archean, and from lower Paleozoic limestones, from which it is not always easily distinguished when the gravels are absent, while the gravels