Maryland Geological Survey 41 



which are about 4000 feet in elevation, serving as the monument that 

 bears witness to the industr}' of tlie rivers of tliis area and time. The 

 Xew Jersey Straits were still open, through which into the Appahichian 

 trough the slowly changing 'fro/iiilolc/il us rarlii/iliis faunas repeatedly 

 migrated. In Maryland one Hnds but little of the life of the southern or 

 Mississippian Sea. 



In the simthem Appalachian trough the greatest abundance and variety 

 of ]\lid(lle Devonian life occur in the Hamilton member of the Korrmey for- 

 mation, tlie equivalent of the Hamilton formation of New York, but this 

 habitat was an unfavorable one owing to the extraordinarily rapid accumu- 

 lation of sand and muds. These faunas were repeatedly snuffed out by the 

 great quantity of silt that settled upon them, and it is pTobable that only 

 during the periods of smaller stream discharge and clearer seas could 

 the permanent region of life — the Atlantic Ocean — again and again dis- 

 tribute its migratory species and the free-swimming larvge of the abyssal 

 more or less sessile forms. The muds and sands finally accumulated to such 

 an extent that the Appalachian Sea was no longer a tit habitat for marine 

 life, and before the close of the Devonian great areas were exposed as 

 river deltas. Any fresh or brackish water or land forms that were stranded 

 or died on these flats were oxidized and completely destroyed by the air, 

 a fact proved by the barren muds and sands, often red in color, indi- 

 cating the completeness with which the carbonaceous materials of the 

 orgajiisms had been removed. Hi places, however, the Atlantic still con- 

 tinued to communicate with the Appalachian trough, even into the time 

 of the next higher series, the Bradford of the Mississippian period, its 

 organic remains being found in northwestern Pennsylvania and eastern 

 Ohio. Subsequent to the Bradford all Atlantic connections ceased in the 

 Appalachian trough, and during the rare intervals when marine waters 

 appeared in Maryland they were derived from the Misvsissippian Sea with 

 Gulf of ^Mexico connections. 



