422 CASTS OF MID FfRROAV?, WAVE LINES. (StC. 



Re>[arks upon Casts of ]Mid Furrows, "Wave Lines, and 

 OTHER Markings upon Rocks of the New York System. 

 By James Hall, of Albani/, X. Y. 



The surface ol' strata in all the slialy or intermingled shaly and 

 sandy deposits, from the oldest of the kind up to the coal, and 

 even in the new red sandstone, present us with many peculiar 

 markings, wliich, for the most part, can be referred to no known 

 organic forms, and from analogy are considered as due to the 

 influence of physical causes in operation at the time of the de- 

 position of the strata. Among these have been recognized the 

 ripple-mark, and the impression of rain-di-ops ; the one indicating 

 shallow water or a chy beach, and the other a condition of soft 

 mud, which could be impressed by the force of rain-drops. The 

 great depth of deposits above these, prove their subsequent sub- 

 sidence, allowing other strata, often marked in the same manner, 

 through many feet in tliickness, to be deposited upon them. 



The most remarkable rock impressions are those of the feet of 

 reptiles and birds, w-liich are likewise often found in connection 

 with those alluded to. 



Besides the markings enumerated, are numerous otliers, which 

 have been referred to Fucoides, or marine vegetation of some 

 kind ; but these are so dissimilar, that they could have been pro- 

 duced only by forms belonging to very different families of 

 plants, if indeed many of them are organic at all. In regard to 

 many of these forms, it is quite CNiident that they are due to inor- 

 ganic or dynamic causes, and not to the influence of organiza- 

 tion: Tlie situation, position, association, and all other circum- 

 stances, prove them to have had this origin. Certain of these 

 are always found upon the under side of hard layers, and always 

 at the junction with a softer one below, a position which corre- 

 sponds with that of many of the fucoides or marine vegetables. 

 These are frequently attached to the lower side of the stratum, as 

 if growing upon a soft bottom, and becoming imbedded in the 

 next deposition. There are also other appearances, which seem 

 to be due to accretionary action, by which irregular markings 



