EjjBLicH.] GEOLOGY CONCLUSIONS. 349 



that the granite, by some vertically-acting force the origin and effect of 

 ■which cannot be discussed here, has been forced upward, may have not 

 only assisted in locally disturbing strata with which it was at one time 

 in no immediate contact, but has actually, by virtue of this force, been 

 brought into contact with such strata. Footing upon the observation 

 of facts that to me cannot be otherwise explained, I see no discrepancy 

 with any well-founded hypothesis that may be universally accepted to 

 regard the' immediate action of the granitic masses as implying the 

 agent of a vertical force to which it must owe its elevation. Examina- 

 tions were made with a view to determine the presence of magnetic 

 iron in the specimens of granite collected in this district, and it was 

 found that not one specimen was without it. As a rule, the light-colored 

 granites, of a more recent date than the red ones, contained more than 

 the latter, a fact that can readily be explained by assuming that their 

 younger existence upon the surface could not admit of so extended an 

 influence of atmospheric agencies upon their constitution, while the 

 older granite may probably owe its decrease in the percentage of magnetic 

 iron, and, on the other hand, its red color, to the action of these agents. 

 By increasing its perceutage of oxygen, the iron compound contained 

 would change in such a manner as to impart to the rock that color 

 which it now possesses. It remains to be stated that there are two ex- 

 ceptions to the rule above given, where in both instances magnetite was 

 contained as a mineral impregnation in the red granite, in the one 

 instance even in crystals of three-fourths of an inch in diameter. 



Of the Silurian formation we have some of the oldest strata, as indi- 

 cated by the comi^aratively unsatisfactory paleoutological remains, and 

 from these upward the Devonian rocks also seem to be represented, 

 although no strict identification was possible. The Carboniferous is 

 well developed, showing great uniformity in the groups of strata. Con- 

 sidering the imperfect evidence derived from the fossil remains below 

 the Arkansas sandstone, there might be some doubt regarding its age, 

 and the question could arise whether it would not be more correct to 

 assign it a position parallel to the " Old Eed" of the Devonian; but, for 

 reasons based upon stratigraphical evidence and the total absence of 

 fossils that might decide, this has not been done. A wide gap now fol- 

 lows, comparing the formations of this district with those analogous 

 from other parts of the world, until the Mesozoic period is reached. 

 The position of this series seems to be as well established as possible 

 with the very meager amount of fossils that has been found. In some 

 of his earlier expeditions. Dr. Hayden has found Fentacrinites in some 

 strata that are recognized as having their position above the so-called 

 " red beds," which would settle the question, leaving ample space, how- 

 ever, for any subdividing of the group. Well-defined and of admirable 

 uniformity in character are the Cretaceous strata, to which the five 

 adopted divisions api^ly without discrepancy. The gradual receding of 

 the formations belonging to this group from the mountain-edge, the still 

 greater development of this feature during the Post-Cretaceous epoch, 

 speak for the gradual rise of the land west of them during a period of 

 time that must be located in the close of the Cretaceous. Apparently 

 a knotty question arises when the age of the "Lignitic" beds is consid- 

 ered ; but undoubtedly future investigations, not merely of the paleou- 

 tological remains, but of the geognostic relations they bear to over- and 

 underlying formations, will tend to clear up any lingering doubts. Those 

 found in our district seem (speaking with all the reserve that a mere su- 

 perficial examination demands) to be of an age which can paleontologi- 

 cally be referred neither to the Cretaceous nor to the Tertiary, analogous 



