Revieius — Recent and Fossil Ripple-marks. 33 



coal districts the seams are much thinner, though often still con- 

 siderable, and the total reserve is still large. Unfortunately a large 

 part of the coal-fields lie under the sea, so that access is rendered 

 more difficult; 



R. H. E. 



VII — Recent and Fossil IIippi.e-marks. By E. M. Kindle. 

 Geological Survey of Canada, Museum Bulletin No. 25. pp. 56, 

 with 33 plates. Ottawa: Government Printing Bureau, 1917. 



I)IPPLE-MAE.KS are of three distinct types: the first is due to 

 \i current action on a sandy bottom, the second to wave action, 

 and the third to the direct action of wind on sand. Mr. Kindle 

 discusses very fully the characteristic features of each type, and 

 illustrates them by means of photographs and profiles of casts of 

 plaster of paris moulds taken directly from ripple-marks. Many of 

 the moulds were actually taken under water, at times at not in- 

 considerable depths, with the aid of ingenious apparatus which the 

 author had specially designed for the purpose. Geologists will be 

 grateful to him for his clear exposition of the subject. Por the lack 

 of some such work geological literature contains many references to 

 ripple-marks which are full of mistakes. A common error is to 

 suppose that fossil ripple-mark is evidence of shore or shallow-water 

 conditions. On the contrary, there is every reason to believe that 

 the action of a storm wind will produce ripple-marks to a depth of at 

 least fifty fathoms of water. The greatest depth at which the author 

 lias obtained a plaster of paris mould was 27 feet. Again, many of 

 the so-called " mud-flows" which have often puzzled geologists are 

 really the marks produced by the mutual interference of two or more 

 currents. 



It is interesting to note that whereas the amplitude of dune or 

 wind ripple-mark shows only slight variation, that of subaqueous 

 current ripple-mark may vary enormously, depending on the load of 

 sediment carried and the velocity of the current. Ripples of colossal 

 size are developed in the Ottawa River during the flood stage over 

 the broad sand-bar at Duck Island. In late summer they are laid 

 bare at low water, and the crests of the ridges are seen to be 30 to 45 

 feet apart and 1 to 2 feet above the troughs. In estuaries subject to 

 strong currents terrace-like ripples are formed which though of 

 remarkable size closely resemble ordinary ripple-marks. 



VIII. — South Atjstealia. 

 A Review of Mining Operations in the State of South Australia 



DURING THE HALF-YEAR ENDED DeCEMBKR 31, 1916. jS^O. 25. 



Compiled by L. C. Gee, S.M., Chief Registrar and Recorder, 

 Department of Mines, pp. 91, with 4 plates and map. Adelaide, 

 1917. 

 rnmS review contains reports on a number of different mining and 

 J. prospecting operations in the State of South Australia. Bores 

 have been undertaken with the object of discovering the westerly 

 extension of the AVallaroo main lode to the Wallaroo Extended 



DECADE VI. — VOL. V. — NO. I. 3 



