Geological Society. 323 



necticut, about eleven miles north of Springfield. The rock con- 

 sists of thin-bedded sandstone with red-coloured shale. Some of the 

 flags are distinctly ripple-marked, and the dip of the layers on which 

 the Ornithichnites are imprinted, in great abundance, varies from 

 eleven to fifteen degrees. Many superimposed beds must have been 

 successively trodden upon, as different sets of tracks are traced 

 through a thickness of sandstone exceeding ten feet ; and Prof. 

 Hitchcock pointed out to the author that some of the beds exposed 

 several yards farther down the river, and containing Ornithichnites, 

 would, if prolonged, pass under those of the principal locality, and 

 make the entire thickness throughout which the impressions prevail, 

 at intervals, perhaps twenty or thirty feet. Mr. Lyell, therefore, con- 

 ceives that a continued subsidence of the ground took place during 

 the deposition of the layers on which the birds walked. 



It has been suggested, but the opinion has not been adopted by 

 Prof. Hitchcock, that the eastward slope of the beds represents that 

 of the original beach. With a view to this question, Mr. Lyell exa- 

 mined the direction of the ripple-marks, and found that it agreed with 

 the dip, or was at right angles to the supposed line of beach ; but he 

 adds, though this agreement presents a formidable objection to the 

 suggestion above alluded to, if the ripples were produced by waves, 

 yet it does not disprove the opinion, as the ripples do not exceed in 

 dimensions those which are produced by sand blown over a muddy 

 beach, and often distributed at right angles to the coast- line. In- 

 stances of this effect of the wind Mr. Lyell has remarked along the 

 shores of Massachusetts. Nevertheless he is of opinion that the 

 rippled layer of sandstone in question contains too much clay to have 

 resulted from blown sand, and he is disposed to think that in most 

 of these localities the strata have been tilted, instances of such dis- 

 turbance having been pointed out to him by Prof. Hitchcock in the 

 state of Massachusetts, and by Mr. Percival near Newhaven in Con- 

 necticut. In reference to this subject, he says, that a few miles from 

 Smith's Ferry a conglomerate, several hundred feet thick, containing 

 angular and rounded fragments of trap and red sandstone, the base 

 being sometimes a vesicular trap and trap tuff, passes upwards into 

 the very flags on which Ornithichnites occur; and from this he infers, 

 hat there were eruptions of trap, accompanied by upheaval and par- 

 tial denudation, during the deposition of the red sandstone. 



With respect to the impressions having been made by birds, Mr. 

 Lyell states, that until he examined the whole of the evidence he 

 entertained some scepticism, notwithstanding the luminous account 

 given by Prof. Hitchcock. In proof of their being the foot-prints Of 

 some creature walking on mud or sand, he mentions, 1st, the fact of 

 Prof. Hitchcock's having seen 2000 impressions, all, like those he had 

 himself examined, indented in the upper surface of the layer, the 

 casts in relief being always on the lower surface ; and 2ndly, that 

 where there is a single line of impressions the marks are uniform in 

 size, and nearly uniform in distance from each other, the toes in the 

 successive steps turning alternately right and left. Such single lines, 

 Mr. Lyell says, indicate that the animal was a biped, and the trifid 

 marks resemble those which a bird leaves, there being generally a 



Y 2 



