800 HISTORICAL GEOLOGY. 



In the progress of the npttirning the sandstone was variouslj^ fractured 

 and faulted ; and the masses into Avhich it Avas thus divided were in part 

 forced over one another, and up whatever surfaces Lay beyond, and thus the 

 monoclinal structure was produced. The abraded surfaces of the beds, 

 extensively exhibited in some regions, indicate that there was a vast amount 

 of intestinal movement as Avell as ordinary faulting. The sandstone should 

 therefore have acquired its greatest thickness, from piling on itself, on the 

 side of the area in the direction of the movement ; that is, on the west side 

 in the Connecticut valley, and on the east, in the Palisade belt. Moreover, 

 the confining slope of the trough on this side would have been an obstruc- 

 tion that would have there increased the fracturing and the amount of piling. 



The lateral thrust Avould have narrowed the belt of deposits of each 

 geosyncline. The amount of narrowing, taking the mean dip of the beds at 

 15°, and supposing no modifying conditions, would have been about 100 feet 

 for every 3000 feet of width. But the piling of the beds referred to above, 

 and the shoving of the beds beyond the limit of the original area or trough, 

 are modifying conditions that cannot be estimated. 



The shallow mass of deposits in each geosyncline had a temperature at 

 bottom possibly of 200° F. or 300° F. ; for, if 10,000 feet thick, the present 

 rate of increase in temperature doAvnward would make the maximum only 

 200° F. This temperature was sufficient only for a partial consolidation of 

 the beds through any siliceous waters that might have been made, and for 

 the reddening of them by the oxidation of any iron present. The movements 

 from lateral pressure against the trough in the earth's crust, in which the 

 beds lay, might have produced their results by molecular transfer in the 

 mass of the crust. But the facts point unquestionably to great and deep 

 fractures. The directions of such fracture-planes would have been deter, 

 mined partly by the positions of the weaker planes in the rocks beneath. 

 Such weak planes may be due to kinds of rocks ; to the foliation or bedding 

 of the rocks ; to earlier fault-planes ; or to preexisting mountain features of 

 the Atlantic border. But their actual positions are not often determinable 

 except so far as they may be inferred from the lines of eruptive rocks. 



Igneous eruptions over the Triassic areas. — The general features of the 

 outcrops of trap over the areas are well displayed in the Connecticut valley, 

 an excellent map of which for the state of Connecticut is contained in 

 J. G. Percival's Geological Report (1842) ; and for the Massachusetts portion, 

 by B. K. Emerson, in the Bulletin of the Geological Society of America for 

 1891. The accompanying map. Fig. 1346, which is part of Percival's, embraces 

 the southern three fifths of the whole area in Connecticut, or the part from 

 the Sound to the latitude of Hartford. Its length is 37 miles, or about 

 one third of that of the whole valley. 



On the map the dotted lines nn, mm mark the outlines of the Triassic area ; outside, 

 both to the east and west, the rocks are crystalline rocks. The heavy black lines rep- 

 resent the outcrops of trap. Commencing at the south, the abbreviations used on it are 

 as follows : N H, New Haven ; pp, bb, dikes of trap outside of the area, on the west ; and 



