REPORT ON FORESTS. 195 



Jurassic Period. Towards the close of the Triassic period 

 great physical changes occurred, of which the extrusion of trap 

 dykes was one of the prominent features. The indications are 

 that that portion of the continent now represented by New 

 Jersey and vicinity was raised to a higher level than further 

 south, for the reason that in this region we find no deposits 

 which can be recognized as Jurassic, while deposits which may be 

 provisionally considered as such occur in Maryland and southward. 

 In New Jersey, therefore, we have a break in the geologic sequence 

 at this point, and in consequence a hiatus in the line of plant 

 development, which, however, has been at least partially bridged 

 by Professor Wm. M. Fontaine* and Dr. Lester F. Ward, f in 

 their studies of the Potomac formation of Maryland. The exact 

 geologic age of the lower strata of this formation has not been 

 definitely determined, but the evidence thus far adduced from 

 the fossil plants indicates a transition from the Triassic flora 

 below to the typical Cretaceous flora above. In this transition 

 flora, accompanying the numerous pteridophytes and gymno- 

 sperms, are many archaic types, mostly of undoubted angio- 

 sperms, in which generic relationships with living plants are 

 more or less definitely indicated under such names as Ficophyl- 

 lum, Sapindopsis, Saliciphylhim, Quercophyllum, Eucalypto- 

 phyllum, &c. A number of living genera are also recognized, 

 such as Torreya, Sequoia, Araucaria, Taxodium, Sassafras, 

 Ficus, Myrica, Sterculia, &c. The number of pteridophytes 

 and gymnosperms, compared with the angiosperms, is about 4 

 to i. The comparatively limited number of modern elements 

 contained in the flora renders any comparison with our living 

 flora somewhat hazardous, so far as any conclusions as to the 

 probable climatic conditions are concerned, but we may safely 

 say that in its general characters tropical or sub-tropical condi- 

 tions are indicated. 



Cretaceous Period. As previously stated, Jurassic strata are 

 wanting in New Jersey, and we find that those which next suc- 

 ceed the Triassic are clays, sands and gravels of Middle Creta- 

 ceous age. This indicates a later submergence of the New 

 Jersey area, when the shore-line was approximately where we 



*"The Potomac or Younger Mespzoic Flora." Monographs of the U. S. Geol. Survey, Vol. XV. 

 f" The Potomac Formation." isth Ann. Rept. U. S. Geol. Survey, pp. 307-397. 



