Ornithichnology. 331 



sumption, shows us that little dependence is to be placed upon 

 such an argument as this, to prove the rock in question, to be new 

 red sandstone. But the Ichthyolites occurring in it, present a much 

 stronger case. They belong to the genus Palaeothrissum, and are 

 found in bituminous shale, or what used to be called bituminous 

 marlite ; and the specimens, both of the fish and the rock, so exact- 

 ly resemble those from the new red sandstone of Mansfeld, in Ger- 

 many, that an able European geologist, to whom specimens were 

 sent, could not distinguish them. This genus, also occurs at Au- 

 tun in France, and at one or two places in Great Britain, in the 

 new red sandstone, and in that alone. How can it be doubted, es- 

 pecially when the other evidence to the same point is considereid, 

 that it is the same rock in Massachusetts, in which they are found ? 

 It ought to be stated, that one of the localities of ornithichnites, 

 occurs only a mile distant from the most abundant locality of ichthy- 

 olites in Sunderland, and almost on the same continuous layers of 

 rock. 



These statements, it seems to me, decide, beyond all reasonable 

 doubt, the geological situation of the ornithichnites that have been 

 described. But if any are not satisfied, it ought still farther to be 

 stated, that no geologist, who has examined the sandstone of this 

 valley, has ever suggested that it is more recent than the new red 

 sandstone. For the most part, they have placed it lower in the 

 series ; regarding it either as the coal formation, or the old red sand- 

 stone. So that all would agree that these ornithichnites are at least, 

 as low down as the new red sandstone. If they are lower, their sit- 

 uation is still more surprising. 



Since the deposition of this sandstone, no geological change seems 

 to have taken place in this valley, except the deposition of a thin 

 and apparently very recent tertiary, or quaternary formation, com- 

 posed of horizontal layers of clay and sand ; and afterwards those 

 diluvial and alluvial agencies succeeded, which have been in opera- 

 tion in every part of the globe. 



Having now given such a statement, as I am able, of the facts in 

 this case, and shown, if I mistake not, the geological position of the 

 ornithichnites, I trust, I may be indulged in a few theoretical consid- 

 erations. 



The circumstances under which these tracks were made, furnish a 

 topic of enquiry that will suggest itself to every mind ; and it seems to 

 me that the true theory on the subject, can hardly be mistaken by 

 any intelligent man, even although not acquainted with the princi- 



