TRIASSIC PERIOD. 419 



from a more complete one of the State, by Percival, gives some idea 

 of their number and position. They commence near Long Island 

 Sound, at New Haven, where they form some bold eminences, and 

 extend through the State, and nearly to the northern boundary of 

 Massachusetts. Mounts Holyoke and Tom are in the system. The 

 general course is parallel with that of the Green Mountains. 



Although the greater part of the dikes are confined to the sand- 

 stone regions, there are a few lines outside, intersecting the crystalline 

 rocks, and following the same direction ; and part, at least, of these 

 belong to the same system. 



Even the little Southbury Triassic region, lying isolated in western 

 Connecticut, has a large number of trap ridges, and such a group of 

 them as occurs nowhere else in New England, outside of the Triassic. 

 Their direction and positions in overlapping series are the same as in 

 the Connecticut valley. 



The trap usually forms hills with a bold columnar front and sloping 

 back ; when nearly north and south in direction, the bold front is to 

 the westward in the Connecticut valley, and to the eastward in New 

 Jersey. It has come up through fissures in the sandstone, which 

 var^d from a few inches to 300 feet or more in breadth. In many 

 cases, it has made its way out by opening the layers of sandstone ; 

 and in such cases it stands with a bold front, facing in the direction 

 toward which it thus ascended. 



The proofs that the trap was actually melted are abundant. For 

 the sandstone rocks have in many places been baked to a hard grit by 

 the heat, and at times so blown up by steam as to look scoriaceous ; 

 and such layers have been actually taken in some cases for beds of 

 scoria. In some places, the uplift has opened spaces between the 

 layers, where steam has escaped and changed a fine-grained clayey 

 sandstone into a very hard rock looking like trap. Occasionally, crys- 

 talline minerals, as epidote, tourmaline, specular iron (hematite), gar- 

 net, and chlorite, are among the results of the heat or hot vapors. The 

 evidences of heat, moreover, diminish as we recede from the ridges. 

 There is no doubt that the sandstone in many places owes its escape 

 from denudation to the firm consolidation it derived from the heat and 

 vapors rising with the eruptions, and to the waters of hot springs then 

 set in action. 



In all the several regions along the Atlantic border, the sandstone strata are in most 

 parts much tilted. In North Carolina, there is generally a dip of 10° to 22° to the 

 southeast (Emmons) ; in Virginia, Maryland, Pennsylvania, and New Jersey, the dip 

 is to the northwest or north-northwest (Rogers); in Connecticut and Massachusetts, to 

 the east or southeast, the amount seldom exceeding 23°. 



Some of the dikes of trap and fissures in the sandstone, in Con- 



