Degembee 4, 1896.] 



SCIENCE. 



811 



tempt to make out the age of formations by 

 the use of such material is too often labor 

 lost and must necessarily be so. As a 

 faithful pupil of Goeppert, one of the fathers 

 of fossil botany, I may perhaps be allowed 

 to say this, especially as it was from his in- 

 struction that I first learned to doubt the 

 value of fossil plants as indices of the past 

 history of the world. Such specimens may 

 indeed aid in marking the continuity of a 

 particular stratum or horizon, but without 

 the reinforcement of higher forms of life 

 <;an do little to determine the age. 



The paleobotanists have certainly failed 

 repeatedly in the past in attempting to de- 

 fine geological horizons by fossil plants 

 alone. Although they have this record as 

 a guide, some of them are still using the 

 same methods, the same material, with the 

 same confidence, that formerly misled their 

 predecessors. In view of this, and of the 

 great importance of the present question, is 

 it too much to ask them to reconsider their 

 verdict as to the age of the Potomac forma- 

 tion? 



Were the fossil plants of the Potomac 



the plants alone cannot finally decide the 

 age. 



POSITION OF JURASSIC STRATA. 



In the geological section. Figure 1, on 

 page 806, the relative position of the Juras- 

 sic deposits of the West is designated, and 

 this will hold good for all the strata of that 

 age in known localities on both flanks of 

 the Rocky Mountains. In the East the 

 position of the deposits here regarded as 

 Jurassic is equally definite, and corresponds 

 strictly to that of the western horizon in its 

 most essential features. A reference to the 

 section in Figure 2, below, will make this 

 clear. This typical section is based on one 

 by G. H. Cook, in the Geology of New Jer- 

 sey,* and represents the successive Mesozoic 

 and more recent formations, from New 

 Brunswick, New Jersey, on a line south- 

 east, through Lower Squankum to the 

 Atlantic. The relative proportions and in- 

 clination of the various divisions cannot, 

 of course, be given accurately in so small 

 a figure. The distance represented by this 

 section is about forty miles. 



FiGUEE 2. — Geological Section in New Jersey, 

 ffl, Triassic; &, Jurassic ; c, Cretaceous; d, Tertiary; T, tide level. 



that have been pronounced Cretaceous un- 

 known, the Jurassic age of this extensive 

 series would have been accepted as a matter 

 of course long ago. The strata themselves 

 lie exactly in the position the Jurassic 

 should occupy. They agree in physical 

 characters more closely with the shallow 

 fresh- water shales and sandstones of the 

 Trias below than with the deep-sea Creta- 

 ceous beds above. Still more important, 

 the animal remains taken together, inverte- 

 brates and vertebrates, indicate one fauna, 

 the Jurassic. Under these circumstances 



In this section, the red Triassic shales 

 and sandstones are shown on the left, 

 highly inclined. Eesting on their eroded 

 surface are the well-known variegated 

 plastic clays, also of fresh-water origin. 

 These strata are nearly horizontal, having 

 a slight inclination toward the ocean. The 

 top of these peculiar clay beds is not defined, 

 but is marked by a change from lacustrine 

 to marine conditions, which clearly indicate 

 deposition in water of increasing depth, and 

 finally deep-sea glauconite strata. These 



*Geological Map, Cretaceous Section 3, 1868. 



