Reviews. 



The Lafayette Formation. By W. J. McGee. Twelfth Annual 

 Report of the U. S. Geological Survey, pp. 347-521, 5 maps, 

 5 plates, 45 text cuts. 



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 phys- 

 ical history of the continent, until the appearance of this work.^ The 

 investigation of the formation was commenced in Mississippi by Pro- 

 fessor 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 mas- 

 sive 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 



' The author had published several advance notices prior to the appearance of the 

 present report. 



435 



