108 The Ottawa Naturalist. [Dec. 



3. The same species. Side view of one of the arms, showing 

 the tuberculate outer surface and the smooth and truncated 

 upper surface of the marginal plates. This is 9 . 5 times natural 

 size. Photograph by Porfessor Hudson. 



4. The same species. View of the same arm, looking down 

 from above, showing the pits in the adambulacrals, and the 

 closely fitting "covering plates." This is 9. 5 times natural size. 

 Photograph by Professor Hudson. 



NOTE ON A RIPPLE-MARKED LIMESTONE.* 



By E. M. Kindle. 



The occurrence of ripple-marks on sandstone is a common 

 phenomenon to every geologist, and nearly every one has 

 observed these beautiful flutings in process of formation on 

 the sands of lake or sea shore. The literature on ripple-marks 

 relates almost entirely to these familiar sand or sandstone ripples. 

 The occurrence of ripple-marks on limestone seems to be a 

 phenomenon of such relative infrequency that it appears desir- 

 able to record an example which has come under the writer's 

 notice. 



The ripple-marks which will be described characterize 

 certain Devonian limestone strata in northern Manitoba. The 

 basin of Lake Winnipegosis is excavated chiefly in limestone of 

 Devonian age, and the principal outcrops of these beds in 

 Manitoba occur around the shores and on the islands of this lake. 

 The best exposures of the Devonian strata about the southern 

 end of the lake, appear on Snake Island. 



This island, as noted by Mr. J. B. Tyrrell 1 , is classic 

 ground in western geology, having furnished the collection of 

 fossils made by Prof. H. Y. Hinde in 1858, which first deter- 

 mined the presence of Devonian rocks in Manitoba, but the 

 ripple-marked limestone appears not to have been noted by 

 previous observers. 



I visited this locality during the past summer, and in 

 company with Mr. A. MacLean examined the interesting ripple- 

 marks which are best exposed on the surface of a large block 

 of limestone which has broken down from the cliff near the 

 northwest corner of the island. This cliff is shown in plate VII, 



* Published with the permission of the Director of the Canadian Geological 

 Survey. 



1 Tyrrell, J. B. Report on Northwestern Manitoba with portion of 

 adjacent districts of Assiniboia and Saskatchewan: Geol. Surv. of 

 1 m., Pt. E, Vol. V, 1889-90-91. (1892) p. 163 E. 



