712 



E. M. KINDLE 



ripple-marks may be related to the relative average depths at which 

 limestone and sandstone sediments accumulate. In other words, the 

 usual large amplitude of limestone ripple-marks may be a function 

 related to the depth of the water in which they are formed. If we 

 apply this as a working hypothesis to the case under consideration, 

 we must conclude that the ripple-marks in the Trenton limestone 

 near Ottawa were formed under water of considerably greater depth 

 than those in the Cambrian sandstone. The presence of long 



Fig. 6. — View showing profusion of crinoidal remains found on the surface of some 

 of the ripple-marks in cement quarry at Hull. Photograph by L. D. Burling. 



crinoid stems upon the limestone ripple-marks is significant in con- 

 nection with the question of the depth of the water under which 

 they were formed. They were developed during an interval when 

 a luxuriant crinoid fauna flourished in this part of the Trenton sea. 

 All of the members of this order which live in the present seas are 

 found, with a very few exceptions, in comparatively deep water. 

 The living stalked crinoids are found chiefly at depths of more than 

 200 fathoms; a few extend into 140 fathoms and a very limited 

 number into 58 fathoms, while one or two species are known 

 in still shallower water. Geologists are accustomed to infer the 



