TABLE I. 



D. 



MUD iUKROWS (I), ANJJ l.MrRESSlONS OF PLANTS (?), IN THE RED SANDSTONES OF THE NORTHWEST SHORE OF 



LAKE SUPERIOR. 



MeJal-ruled on Steel, iVom tlie Original Specimens. 



'ab. I. D, Fig. 1. This is a perfect fac simile of markings or furrows, in bold and high relief, of a quarter to half an inch, on a 

 slab of argillaceous gritstone. Whether it has been produced by tidal action, on a muddy, sandy sea- 

 shore, I am hardly prepared to say. It has not at all the usual form of ripple-marked sandstones, such 

 as are common on the south shore of Lake Superior. From the peculiar pendent and lengthened 

 mammillary appearance of some of the furrows, and the resemblance of the rock to volcanic grits, I 

 am rather disposed to the belief that the material of which the rock is composed was once volcanic 

 mud, and that, while in a viscid state, it congealed suddenly, or became fixed in the very act of flowing 

 down the hillside ; transmitting to us a lapidified memento of the action of some mud volcano in the 

 vicinity. 



Fig. 2. The origin of this curious fossil has been a great puzzle. Most persons, regarding it at first, might be 

 tempted to consider it an ornithichnite ; and, indeed, a very close similitude can be observed to a 

 bird-track, in the general contour of the impression. A resemblance can also be traced, in certain 

 parts of the fossil, to the beak and muscular impression of an Oslrea. Nevertheless, after having 

 carefully studied this specimen in connexion with others of a siraiiar character from the same locality, 

 in all its variable forms, we are led to the conclusion that it had no such origin ; but has probably 

 been derived from some marine vegetation, of a curious and very anoinalous form. 



