CAMBRIAN AND ORDOVICIAN RIPPLE-MARKS 711 



of the Clinton limestone which have crests 18-30 inches apart 

 with troughs 2-4 inches deep. Foerste^ mentions ripple-marks in 

 the Springfield dolomite, west of Peebles, Ohio, one-fourth mile. 

 Professor Prosser^ states that the ripple-marks at this locality occur 

 in two beds. ''In the lower layer the crests of the ripples are 

 22 inches apart and the trough 4 inches deep. In the upper layer 

 the crests are 45 inches apart and the troughs 4I inches deep." 



In the Devonian, I am acquainted with but three examples^ of 

 ripple-marked limestones. Each of these shows an amplitude of 

 2 feet or more. 



The only notice of Mesozoic limestone ripple-marks^ which has 

 come to my attention records the occurrence of ripple-marks in 

 limestone of Jurassic age in Utah with an amplitude of 6-12 inches. 



The examples cited above from the literature of limestone 

 ripple-marks plainly indicate the large size usually attained 

 by ripple-marks in pure limestone. It must be noted, however, 

 that ripple-marks of small size also sometimes occur in limestone. 

 A photograph of ripple-marks on a dolomitic limestone with a 

 smaller amplitude than the sandstone ripple-marks reproduced in 

 this paper has recently been published ;^ and Miller^ mentions Ordo- 

 vician examples with an amplitude of 1-2 inches. Foerste'' has 

 observed that large and small limestone ripple-marks in the Ordo- 

 vician of the Ohio valley are seldom associated but confined to 

 distinct horizons. One must therefore conclude that the generally 

 larger size of limestone as compared with sandstone ripple-marks 

 results from some factor other than the different physical character- 

 istics of the two kinds of rock. It seems probable that the explana- 

 tion is to be sought in the fact that limestones are generally formed 

 somewhat farther from the shore and in deeper water than sand- 

 stones. The different average amplitude of sandstone and limestone 



^ Jour. Cin. Soc. Nat. Hist., XVIII (1896), 167. 

 ^ Letter to the writer, February 6, 1914. 



3 One of these has been described {Ottawa Nat., XXVI [191 2], 1-3, PI. 7). 



4 G. K. Gilbert, Science, III (1884), 375-76. 



5 Kindle and Taylor, Folio U.S.G.S. No. igo (1913), PL 25. 

 ^ Bull. N.Y. State Mus. No. 135 (1910), p. 36. 



" Letter to the writer. 



