Ornithichnology. 329 



However strenuously, geologists, a few years ago, contended for the 

 perfect identity of the rock formations of different continents — this 

 opinion, especially in the case of the secondary and tertiary rocks, 

 is now abandoned. All we can hope for, in respect to two such 

 rocks, in different countries, is, that there may be so much similar- 

 ity between their lithological characters, mineral contents, and or- 

 ganic remains, as to show that they were the result of similar 

 causes, and produced under similar circumstances as to tempera- 

 ture, climate, &ic. In respect to the sandstone of the valley of 

 the Connecticut, on which these Ornithichnities occur, there are 

 peculiar difficulties in determining precisely its position on the ge- 

 ological scale. But having examined it with no small care for the 

 last twenty years, with reference to this very point, I have come to 

 the full conviction, as above expressed, that at least the higher beds 

 of this sandstone belong to the new red sandstone of De la Beche 

 and other geologists. The reasons of this opinion I have given in 

 full in my report on the geology, &£c. of Massachusetts, made to 

 the government of that state. But it may be desirable to give a 

 summary of these reasons in this place. 



The sandstone in this valley extends nearly one hundred miles, 

 from New Haven in Connecticut to the north Hne of Massachusetts, 

 varying in width from eight to twenty four miles. It is divided by 

 one or two ridges of greenstone, protruded through the sandstone, 

 and running nearly north and south. The strata of the sandstone 

 have a general easterly dip, varying from 5° to 30° ; so that the 

 lowest or oldest portions of the sandstone lie along the western side 

 of the valley. These lower strata consist, for the most part, of 

 thick layers of red sandstone, not much diversified in appearance. 

 But the upper strata, that is, those on the easterly side of the green- 

 stone ranges, consist of slaty sandstones, red and grey conglome- 

 rated sandstones, very coarse conglomerates, shale, and perhaps red 

 marl,* with occasional beds of fetid limestone. These are interstra- 

 tified in almost endless variety. Now as to the lower strata, some 

 geologists have supposed that they belong to the old red sandstone ; 

 and perhaps they do : but as none of the Ornithichnites occur in these 

 strata, we need not discuss this question. In endeavoring to show 

 that they are the equivalent of the new red sandstone, I confine my- 

 self, therefore, entirely to the upper strata. ' 



* The red sandstone at Hartford, is decidedly marly — it effervesces with acids 

 and even contains numerous veins of calc spar. — Ed. 



Vol. XXIX.— No. 2. 42 



