THE ACADIAN TRIASSIC 267 



ORIGIN 



The basalt unconformity of the Acadian Triassic always shows 

 upturned and beveled rocks overlain by Newark sandstones or 

 conglomerates with bedding parallel to the underlying erosion 

 surface. This fact indicates that the Newark sediments were 

 deposited on a peneplain, as has been found the case in the 

 Connecticut 1 and Richmond 2 areas. 



On this peneplain, an orographic basin was formed, and into 

 the geosynclinal area sediments were brought from all sides. An 

 equilibrium between the rate of sedimentation and of subsidence 

 of the geosyncline appears to have been reached when the Blomidon 

 shales were deposited at the top of the Annapolis formation. 



The Wolfville sandstone at the base of the Acadian Newark 

 shows red sandstones and occasional conglomerates and shales, 

 in general evenly bedded. The pebbles in the conglomerates are 

 stream-worn, but are frequently subangular. The character of the 

 Quaco conglomerate has been sufficiently treated. The Wolfville 

 sandstone indicates stream transportation, with deposition in 

 flood-plains, and perhaps in past in broad alluvial fans. 



The Blomidon shales are generally evenly bedded, but show 

 occasional ripple or current marks, and rarely mud cracks. The 

 presence of Estheria indicates temporary bodies of water. Flood- 

 plains of mature rivers would furnish the necessary conditions for 

 the deposition of shales, with cut-off lakes in which the crustaceans 

 could live. 



The red color of the Annapolis formation evidences long oxida- 

 tion of the iron during transportation and deposition. 3 The white 

 or gray color indicates a lack of hematite, and the green color is 

 caused by the presence of chlorite. 



The climate during the deposition of the Annapolis formation 

 was apparently hot and dry, with occasional floods. The presence 

 of calcite in nearly all the sediments, and the scarcity of arkose, 



1 W. M. Davis, U.S. Geol. Surv., 18th Ann. Rept., 1898, p. 20. 

 2 N. S. Shaler and J. B. Woodworth, U.S. Geol. Surv., igth Ann. Rept., 1899, 

 p. 408. 



3 J. Barrell, "Relation between Climatic and Terrestrial Deposits," Jour. Geol., 

 XVI (1908), 159-90, 255-95, 363-84. 



