CONTRIBUTIONS TO PALAEONTOLOGY. 95 



rine origin. On the northeast, however, the system begins with 

 shore-derived sedimentary deposits ; and these sediments contain 

 remains of land-plants, even to the base, and it may be uncertain 

 whether some of these do not occur in strata of the subjacent 

 Upper Silurian rocks. 



Owing to this great accumulation of land-derived materials in 

 the northeasterly extension of the lower part of the system, while 

 the same epoch was mainly filled by marine deposits farther to the 

 ■west, we have there the advent of the Devonian marked by its 

 flora, while it is only in the second epoch of its duration that the 

 Devonian of New-York is characterized by the presence of land- 

 plants. It therefore happens that the plants of the New-York De- 

 vonian are of the middle and upper divisions of the system, the 

 only evidence of the sedimentary deposits of the first epoch being 

 found in the Cauda-galli grit (a fine gritty shale); and it is 

 probably here, if at all, that we shall find evidences of the older 

 Devonian flora. 



Farther to the west we have, both in the fauna and flora, some 

 evidence of another epoch which may bring up the series to the 

 Carboniferous period ; but at the present time, w^e have not the 

 means of speaking with definiteness on this point. Moreover these 

 differences may be due to local causes within the limits of the 

 region investigated ; and in the present state of our knowledge, 

 it would be unsafe to draw a conclusion, till farther investigations, 

 now in progress, shall have been completed. 



In like manner the Carboniferous period of the northeastern and 

 middle portions is ushered in by a great accumulation of land- 

 derived materials charged with the remains of the luxuriant flora 

 of the period ; while in the western extension of the system we 

 find the period beginning with great accumulations of marine 

 deposits, mostly calcareous, and everywhere marked by the pre- 

 sence of marine fossils. 



In the distribution of sedimentary materials, the Devonian 

 System presents conditions parallel and similar to the great se- 

 dimentary system of the Coal measures. It has its greatest de- 

 velopment in thickness at the Northeast, gradually diminishing 

 in a southwesterly direction, until it is reduced to a few feet of 

 shale. In like manner, its most abundant flora has been found in 

 the Northeast, where the accumulations of the system are far 

 greater than in any part of the country west of the Appalachians. 

 The same conditions have existed, and the same changes have 

 taken place, from the commencement of the great sedimentary 



