LIBRARY 



1916] The Ottawa Naturalist. 



A PRELIM IX ARY PAPER ON THE ORIGIN AND CLASSI- 

 FICATION OF INTRAFORMATIONAL CON- 

 GLOMERATES AND BRECCIAS. 



By Richard M. Field, Agassiz Museum, Cambridge, Mass. 



(Continued from page 36.) 



The author shows that in ground plan these structures are 

 quite similar to mud-cracks, and that they may be accounted for 

 by the excessive dessication of limy sediments or clay-like material 

 which has been preserved above water level for a sufficient 

 period of time to permit of an abnormal deepening of the surface 

 mud- cracks. Should the spaces or cracks between successive 

 layers of such columnated limestones become impregnated with 

 a subsequent deposition of limy, or even sandy material, an in- 

 teresting type of intraformational breccia would probably be 

 formed. 



Hyde (6) describes a peculiar limestone conglomerate 

 from the so-called "fresh-water" horizon of the Ohio coal mea- 

 sures. He writes: "after complete evaporation and cracking 

 of the limy surface, it is necessary to suppose that there was a 

 submergence in order to account for the matrix of small frag- 

 ments and shells in which the pebbles all rest. * * * * If, 

 after the conglomerate was completely formed, the deposition 

 of limestone had been resumed instead of a soft shale, the 

 result would have been a typical intraformational conglomerate 

 of a thinner type, in which the structure would probably have 

 been so obscured that a detailed study would have been im- 

 possible, or only possible with a great amount of labour." 



Bioglomerates. 



There is some evidence that certain intraformational con- 

 glomerates may have been formed partly by organic agencies. 

 Their origin may have been the result of either plant or animal 

 (?) activities, and furthermore, the organisms may have had 

 either a direct or indirect structural influence. Certain so-called 

 "limestone conglomerates" are svipposed to be composed of 

 fossil organisms. Thus, Seeley (7) describes conglomerates 

 from the Beekmantown of the Champlain valley as having their 

 pebbles formed from sponges, a new genus, which he called 

 Wingia. Brown (8) describes certain conglomerates at Belle- 

 fonte as due to the action of lime-secreting algae. He notes 



