52 The Ottawa Naturalist. [June-July 



wise conglomerates." It is conceivable that conditions suitable 

 for the formation of such "edgewise conglomerates" would 

 probably be more or less local within the whole disturbed zone 

 that is, that a typical arrangement of the phenoclasts might 

 not exist throughout the intraformational glomerates. Walcott 

 does not mention the possible effect of the scouring action of 

 tidal currents upon a previously mud-cracked surface. A tidal 

 flat whose sediments were composed of a limy mud, when des- 

 sicated, would, if disturbed by a subsequent and sufficiently 

 powerful tidal action, yield a quantity of tough, not brittle, 

 phenoclasts, which might be redeposited with little or no signs 

 of attrition except at the edges. Ripple-marked and mud- 

 cracked bars and flats are very apt, at the present day, to be 

 dissected by shallow currents, and these channels should act as 

 catch basins into which the phenoclasts derived from the mud- 

 cracked zone are tumbled by the onrushing tide. Agassiz (13) 

 noticed that the lime-mud deposited by the waves of Florida 

 hardened within a few hours to such a degree that it made a 

 ringing sound when walked upon. This scaly deposit becomes 

 exceptionally brittle between tides, and might, under certain 

 conditions of deposition, be broken up by the advancing waves 

 and re-deposited in much the same manner as suggested by 

 Walcott. 



(To be continued) 



NOTE. 



The Editor of The Ottawa Naturalist has frequently 

 been asked, by members of the Club, for information on Nature 

 Guide books. He has thought it advisable to list the pocket 

 guides which are now available, and which may be obtained at 

 The Book Store (A. H. Jarvis), Bank St., Ottawa, or from 

 James Hope & Sons, Sparks St., Ottawa. These are as 

 follows : 



The Bird Guide Land Birds 



The Bird Guide Water Birds 



The Flower Guide 



The Tree Guide 



The Butterfly Guide 



The Animal Guide 



All of the above are "beautifully illustrated in colours. 

 They are invaluable to the nature lover, and in price are 

 $1.00 each. 



