302 BULLETIN OF THE 



only an inch from the contact, and the baking as reaching only a foot 

 (19G). Under Mount Tom (B), the baking reaches three feet or more. 

 Under the First Mountain trap at Patersou (L), the alteration is dis- 

 tinct for several inches. 



The different effects in these contrasted cases evidently depend on the 

 manner and rate of cooling. The intruded sheets must have cooled 

 slower, and entirely by conduction through the enclosing rocks, and 

 hence produced more baking than the others. The difference in the 

 baking effects of different intruded sheets can probably be largely re- 

 ferred to the variations in the composition and the amount of moisture 

 present at the time of intrusion. 



Tilting of the Sandstones and Traps. — The remarkable monoclinal 

 structure of several of the Triassic belts has given sise to five supposi- 

 tions : first, that the present is the original position of deposit ; second, 

 that the originally flat layers have been tilted into a monoclinal without 

 faulting ; third, that certain paired belts are lateral remnants of a broad, 

 eroded anticlinal ; fourth, that the present position is the result of re- 

 peated faults and moderate folds ; fifth, that a tilting was in progress 

 during the deposition (Cook, h, 174; c, 34). I am unable to give any 

 evidence for or against this last proposition. 



Before speaking of these theories we may note the structure of the 

 several Triassic belts ; for some of them do not present any very peculiar 

 features in the position of their strata. On Prince Edward Island the 

 formation shows repeated faint folds (Dawson and Harrington). Around 

 the Bay of Fundy there is an unsymmetrical synclinal, with the greater 

 visible part on the southeast. The Connecticut valley belt has a pre- 

 vailing dip to the eastward, but with significant exceptions. The long 

 strip from the Hudson extending almost continuously to the Dan River 

 in North Carolina has a similarly prevailing dip to the northwest or 

 west, but also with certain irregularities. The Richmond coal field is a 

 synclinal, strongly faulted (W. B. Rogers and Heinrich). Two patches 

 north and east of it, and the Deep River strip reaching into South Car- 

 olina, dip to the east or southeast (Heinrich and Kerr). 



First Theory. — H. D. Rogers first thought that some external force 

 was responsible for the tilting {a, 160), but soon replaced this supposi- 

 tion with the theory that the several sandstone belts from the Dan River 

 to the Hudson had been deposited with their present oblique dip in a 

 noble river that rose in the mountains of North Carolina and flowed 

 northeast to the ocean about New York Bay , that the occasional rever- 

 sal of dip was produced by eddies in the great current ; and that the 



