'^Vi 



300 



BULLETIN 0^ THE 



creases in thickness or disappears entirely in going south, and the range 

 is continued for a time bj a varying number of smaller sheets. So at 

 Turner's Falls (A), the southward ending of the first and second poste- 

 rior ridges seems as well explained by the giving out of the trap at the 

 edge of its flow-area, as by the faulting suggested by Emerson. At 

 West Springfield (C), the composite structure of the second posterior 

 trap is well shown. In New Jersey the irregularities in the columnar 

 structure of the Newark Mountains at Paterson and Little Falls (L) may 

 be perhaps explained by supposing each mountain to be the product of 

 several consecutive flows. It seems, therefore, probable that the long 

 trap ranges represent a period of volcanic activity, rather than a single 

 violent outburst, preceded and followed by periods of shorter or less in- 

 tense activity represented by the anterior and posterior ridges. This is 

 shown in Connecticut far better than anywhere else, and is beautifully 

 illustrated by Percivai's remarkable map. 



The importance of the overflow trap ranges as marking horizons iu 

 the deposit of the sandstones will be referred to later. 



Ilfect of the Trap on the Sandstone.^ • — A metamorphic effect is gen- 

 erally attributed to the trap, by which the sandstone iu its neighborhood 

 has been indurated and changed in color to a greater or less extent. 

 The most exaggerated form of this idea ascribed the general red color 

 of the whole formation to the effects of trap heat (Hitchcock, d, 242 ; 

 sec also Percival, 430, and Dana, c, 420) ; but as red sandstones are 

 common in other regions far from any contemporaneous or subsequent 

 igneous action, it is more probable that their color here as well as there 

 is essentially due to conditions of weathering at the time of deposit. 

 Whether the contemporaneous volcanic action in the Conncicticut valley 

 aided the coloring of the sandstones or not, is difficult to say; for bright 

 colored strata are found far from and near to the horizons of the vol- 

 canic rocks. _ But, as a general rule, the baked strata near the trap 

 are not so red as the unaltered layers farther away. Above and below 

 the Palisade trap sheet (H), the rocks were black, gray, or dull reddish- 

 , brown, but not strong- or bright red as is common elsewhere. Under 

 Mount Tom (B), the sandstones near and at the contact were gray or 

 dull greenish-gray. Along the Delaware (0, V), the layers nearest the 

 trap sheets or masses were black or dark gray ; the red strata appeared 

 only several hundred feet on one side or the other, so far as seen : these 



* T have not yot had time to examine closely the inineralogioal changes produced 

 by the trap ; some of these, as shown by specimens collected during the past sum- 

 mer, are very striking. 



