If there is one canon in gsology more firmly established than another, it is that fossils indicate a certain definite time in the earth's history, that the various species which they represent appeared, lived, and died out at certain definite times, and that, therefore, fossil evidence has come to be considered the most trustworthy of all evidence as an index to the age and succession of the various rock-formations. In fact, that, as Dr. Mantell put it, fossils are the “Medals of Creation.” Associated with this there is another belief, viz., that the various formations succeeded each other in a certain distinct order, one at a time; that each formation was newer than that below, and older than that overlying it, but was contemporaneous with neither. With these beliefs, it appears, however, that Sir Archibald Geikie does not agree, at least, judging from the third edition of his “Text Book of Geology,” 1893, according to which fossils cannot be depended on as indications of the age of rocks, as they may be found in formations to which they do not really belong; and that the difference between two formations may be geographical rather than geological, as two entirely separate formations may have been formed contemporaneously in different, though possibly neighbouring, geographical areas. Thus, at page 665, it is stated that in Bohemia and Russia some of the most characteristic Upper Silurian organisms are found beneath strata full of Lower Silurian life forms. At page 760, when speaking of the close This 250-word extract was created in the absence of an abstract