424 CASTS OF MUD FURROAVS, WAVE LINES, &C. 



forms mc, arc of frequent occurrence in the new red sandstone 

 series. 



In the strata exhibiting these peculiar appearances, I have 

 never observed the ripple-mark, although it frequently occurs but 

 a few feet below or above, and always within a short distance, 

 indicating that the markings, whatever may have been their 

 origin, were produced in shallow water, at least. 



Associated with these mai'kings is another kind, which thus 

 far I have been unable to refer to any known cause. They con- 

 sist of a series of minute parallel ridges, or extremely low ter- 

 races, not more than an eighth of an inch broad, and one quarter, 

 of this height, in truth, barely perceptible, as having this form. 

 But from the fact of having noticed them in the Portage group of 

 New York, and seeing the same in the collection made by Prof. 

 Hitchcock from the new red sandstone, it seems that they were 

 due to some cause operating in the same manner at these remote 

 periods, and in both cases they are in conjunction with those 

 previously described. 



Casts of Mud Furrows, grooved and striated Surfaces. 



The kind of markings most numerous in these rocks are the 

 straight ridges of various lengths, which are usually referred to 

 fucoides as their origin. There are, however, many attendant cir- 

 cumstances, which prove them to be the productions of a different 

 cause. The fucoides, with no determinate general du*ection, are 

 either straight or curved ; they are usually short, and rarely ex- 

 ceed two or three feet in length. The markings in question have 

 all a uniform du-ection or nearly so, and can often be traced many 

 feet; they ai-e round or angular, the two kinds sometimes ap- 

 pearing together upon the same slab. They ai-e always upon 

 the under surfaces of strata, being attached to a hard layer which 

 rests upon a soft one. 



In dimensions, they vary from tlie diameter of half a foot to 

 that of half an inch, and we find innumerable instances where 

 they present all the appearances of casls of strise or shallow 

 grooves, very much as if an impression were taken from the 

 grooved and striated surfaces of glacial fuiTowed rocks. 



