On the Trap Tuff of the Connecticut Valley. 205 



considerable distance from the ridge of trap, so as to dip 45°. 

 But at this place is another fact still more conclusive to prove the 

 elevation of the strata since their deposition. Those strata, dip- 

 ping about 45°, are often covered with the most perfect foot- 

 marks in connection with raindrops, and not one of them have I 

 ever seen in the least distorted, as if the animal had walked on a 

 slope. The mud was so delicate as to retain the impressions of 

 each phalanx of the foot most perfectly, and yet it has not yielded 

 at all laterally. No one at all familiar with the tracks of living 

 or extinct animals, can doubt that the surface must have been 

 nearly level when these markings were made. The same is 

 essentially the case at the Horse Race, three miles farther up the 

 stream, and indeed at almost every locality of footmarks the 

 slope of the strata appears to me too great not to have shown the 

 slidings of the animal, if he walked upon it at the same dip which 

 it now has. For I have some examples where the effect of walk- 

 ing on an inclined surface is manifest ; and yet at that locality the 

 dip rarely amounted to 10°. On the west side of Connecticut river 

 in Northampton, where are numerous footprints of the huge Bron- 

 tozoum giganteum, a majority of the rows of tracks cross the 

 strata at right angles to the strike ; so that if the strata had their 



present dip at that time— which is about 12° — either the animals 



must have walked so high up the bank that no tide or other rise 

 of water could have covered them, as must have been done to 

 bring over a layer of mud, or the strata must have had a less in- 

 clination than at present ; since some of these rows are several 

 rods long. The latter supposition seems to me to be the true 



and 



up- 



per side of the trap ranges that the footmarks occur, doubtless be- 

 cause the water was too deep when the rock was soft. My ' 



formed 



per. 



so 



as to form a low mud or sand beach, whither the birds resorted, 

 and over which the water frequently flowed, loaded with silt. 

 As successive masses of trap were protruded, successive deposits 

 y°uld come over it, on which other tracks might be formed ; and 

 11 seems to me that in this way we might explain their occur- 

 ence upon successive layers, to a considerable thickness, without 

 Porting, as Mr. Lyell does, to subsidences. And yet when vo - 

 came agency was so common as we know it was during the vol- 

 ea mc period, vertical movements of the surface must have been 



a common occurrence. . , , 



Hut I have wandered somewhat from the subject m hand ; and 



t0 return, it seems to me we have decisive proof that the protru- 



S»°& of the principal ranges of trap constituting Holyoke and 



1 °m, must have been the last of the changes that brought the 



