1893.] ^^^ [Lyman. 



usually given to any single formation ; but, on the other hand, that there 

 is no sufficient reason yet to believe that all the rocks do belong to one 

 paleontological group or formation. The comparatively few fossils found 

 have hitherto been ascribed indiscriminately to the whole so-called forma- 

 tion, without any exact knowledge of the relations of beds of different 

 localities to one another. Perhaps too great reliance has been placed in 

 the capacity of fossils to indicate the geology of a vast series of beds in 

 great measure devoid of them ; and the more laborious, purely geological 

 methods of combining numerous observations of dip, strike and eleva- 

 tion, with the help of topographical indications, have long been neglected, 

 because there was likely to be no sufficient immediate economic return. 



At length, however, the series has been practically worked out by pro- 

 ceeding throughout from one exposure to another near it ; instead of simply 

 assuming a nearly constant dip in one northwesterly direction and estimat- 

 ing the consequent total thickness from the whole breadth of the region 

 filled by the beds. It has now become possible to ascertain from what part 

 of the series the different fossils of the region have come, at least in Eastern 

 Pennsylvania ; and it is seen that nearly all of them have in reality been 

 taken from one small portion, although they have been supposed to indi- 

 cate the age of beds many thousands of feet above or below. It is also 

 seen that the geological structure is not so extremely simple as it was 

 formerly supposed to be ; and that no set of straight parallel faults could 

 have diminished to the desired extent the apparent thickness of the series 

 of beds in Eastern Pennsylvania, for the beds curve strongly and exten- 

 sively in many directions. 



It has, however, long been known that, in the midst of the New Red 

 there, an island, so to speak, of ancient Paleozoic rocks occurs. It was 

 never certainly known, to be sure, whether it was really an island in the 

 New Red sea, with New Red beds of equal age north and south of it ; or 

 had later been thrust up through the New Red beds (or remained fixed 

 while tlie New Red beds on the south sank down) , so as to occasion a great 

 disparity in the age of the beds of the two sides. Now it is positively known 

 that there is such a great difference, and that the New Red beds to the 

 south are several thousand feet higher in the series than those on the 

 north. The line of the southern edge of the ancient island continues 

 westward as a great fault ; but far from parallel to the strike, and conse- 

 quently not helping much, if at all, to diminish the great apparent thick- 

 ness of the New Red. The fault is there the more obvious from a marked 

 difference in the color of the rocks on its two sides. 



But at the eastern end of the island of ancient rocks, just in the edge 

 of New Jersey, the circumstances are somewhat different. There the 

 strike of the beds on the northwest and on the southeast is nearly the 

 same ; and, moreover, the beds of both sides are mainly red ; and they 

 are, besides, in general rather soft shales. Consequently, without the 

 proof given by the observations in Pennsylvania, or perhaps by some not 

 yet made in other parts of New Jersey, it would be extremely difficult, if 



