1912] The Ottawa Naturalist. 109 



figure 1. One of the large limestone blocks which has 

 fallen from the face of the cliff, exhibits the large clearly moulded 

 ripple-marks shown in figure 2. The crests of these are two 

 feet apart, and rise about one and one-half inches above their 

 troughs. The ripples curve slightly in crossing the surface of 

 the limestone. The rock on which they are impressed, is a 

 comparatively pure non-magnesian limestone. The surface of 

 the ripple-marks show great numbers of finely comminuted 

 shell fragments. These small fragments of various kinds of 

 molluscan shells, comprise a large share of the material com- 

 posing the limestone in the middle third of the cliff section in 

 which the ripple-marks occur. These broken shell fragments 

 thus strongly supplement the evidence of the large ripple- 

 marks in indicating vigorous disturbance by wave action of 

 the sea bottom in which they originated. Beyond this fact, 

 it is perhaps not safe to make any deductions regarding the 

 phvsical conditions under which these ripple-marks were pro- 

 duced. It is clear that the water was of sufficiently moderate 

 depth to permit wave action to agitate the bottom, but it does 

 not follow on the other hand, that the sea was extremely shallow. 

 Nor is any valid ground afforded for the assumption of beach 

 conditions which the discussion of ripple-marks presented in 

 some texts' 2 might lead one to make. It has been shown by 

 Mr. A. R. Hunt 3 and others that "ripple-marks occur at 

 much greater depths than is commonly supposed." Dana 4 has 

 has stated that "ripple-marks may be made by the vibration of 

 -3- waves even at depths of 300 to* 500 feet." The unusually 

 large size of these ripple-marks suggest water of greater 

 depth than that which develops the ripple-marks seen along 

 many beaches. Hunt's observations have shown that thousands 

 of specimens of marine shells are sometimes killed in six fathoms 

 of water by wave action. The same observer has found evidence 

 of much damage to shells living in fifteen fathoms from the same 

 cause"'. The broken shell material in these limestones might 

 therefore have been produced in water a few fathoms in depth. 

 The limestones which immediately follow the ripple-marked 

 beds in the cliff section of Snake Island show but little frag- 

 mental material, the fossils contained in them being in a good 

 state of preservation. Ripple-marks appear to be absent from 

 these upper beds. 



2 LeCont states (Elements of Geology 1888, p. 3a), "By means of 

 these characteristics (ripple marks) of shore deposit, many coast 

 lines of previous geological epochs have been determined." 



3 On the formation of ripple marks: Proc. Rov. Soct. Lond., Vol. 

 XXXIV, p. 8, 1S83. 



4 J. D. Dana, Manual of Geology 2d ed. p. 665. 



5 Op. cit, pp. 8, 12. 



