Sand Formation of the United States. 249 



Now, if we cross the Delaware river to MuUica Hill, (about twenty- 

 miles in a northeasterly direction) we shall find similar mineralogical 

 appearances with those last named, sand, gravel and some clay, (but 

 of a mixed brown and green color,) and crowded with the charac- 

 teristic fossils of the marl-region. Here mineralogical appearances 

 are therefore too variable to be relied on, especially where fossils are 

 abundant. The latter must prove one thing or the other ; and I am 

 disposed to take them at their full value until we can find a better 

 substitute. 



Prof. Eaton informs me that he long ago convinced himself " that 

 European strata present more recent characteristics than tlieir equiva- 

 lents in America." If this position can be proved to be a fact, it will 

 settle an important question in Geology ; but when we see so great 

 an analogy between the two continents in the other formations, we 

 should be cautious in admitting so great a variance in this one. 



Time does not permit me to pursue this subject farther at present; 

 but I am convinced that enough has been said, (particularly if consid- 

 ered in reference to the annexed plates,) to prove to the reader the 

 striking affinity that exists between the organic remains of the Amer- 

 can ferruginous sand, and those strata which constitute the great 

 chalk series of Europe. 



I have not yet been able to give any additional attention to the 

 plastic day formation of our coast ; and I trust this division of Amer- 

 ican geology will fall into other and abler hands. 



Explanation of the Plates. 



PLATE 1. 



Fig. 1. Belemnites americanus ; natural size, but an uncommonly large individual. 



2. Transverse section of the chambered portion of the same fossil. 



3. Same species, subfusiform. 



4. Belemnites ambiguus, something larger than natural. 



5. Transverse section of same specimen, natural size. 



6. Baculites ovatus, showing the concentric rings. 



7. Transverse section of the same fossil. 



8. Same species, in which the rings are obsolete. 



9. 10. Anthophyllum atlanticum. Varieties. 



PLATE 2. 



Fig. 1. Ammonites placenta, taken from a specimen fifteen inches in diameter. 



2. Transverse section of the same fossil. 



3. Septa of the same fossil, natural size. 



4. Ammonites delawarensis. 



Vol. XVIIL— No. 2. 32 



