1916 The Ottawa Naturalist 65 



two principal factors controlling the formation of such a glo- 

 merate : 



1 . Alternation of the conditions of deposition. 



2. Dessication. 



Figure 3 of this article is a diagramatic summary of 

 the argument for a classification of sedimentary rocks, and 

 especially of intraformational glomerates, according to the 

 sequence of formative events which they have undergone. The 

 figures are more or less diagramatic, and no attempt has been 

 made to draw an accurate picture of each type. The reader 

 may consult the various descriptions for accurate illustrations. 

 Seven types of glomerates are represented in the columnar sec- 

 tion, six intraformational and one interformational. In order 

 to make the comparisons of the six intraformational glomerates 

 relatively the more graphic, they are all supposed to have formed 

 within a single formation, characterized by the index fossil 

 Ophileta complanata. 



Beginning with .4 time, we have deposition of pure lime- 

 stone until B time, which commences with alternating deposi- 

 tions of pure and shaly limestone, followed by mud-flat condi- 

 tions with dessication and the formation of mud-crack zones 

 or stratified breccias. Here the phenoclast b is practically of 

 the same age as the cement or matrix. During the rest of B 

 time, marine currents are dominant and form edgewise glom- 

 erates, whose phenoclasts of the b' type have been carried a short 

 distance and slightly abraded, so that they are slightly older 

 in relation to their matrix than those of the b type. From the 

 close of B time to the beginning of D time, pure, structureless 

 limestone is laid down. During D time conditions are favorable 

 for the formation of bioglomerates. Here again, as in the case 

 of early B time, the phenoclasts are formed in place, and are 

 practically contemporaneous with the cement. Through E we 

 have a period of pure limestone deposition, except during the 

 middle when shale was formed interstratified with the limestone. 

 In F time we have the formation of a limestone conglomerate 

 whose phenoclasts e are true water-worn pebbles derived from 

 the subjacent zone E. Obviously the pebbles of this conglom- 

 erate were formed long before they were deposited, and long 

 before the ensuing lithification of the mass. Compare the pebbles 

 of this type with the phenoclasts of the preceding types. During 

 G time there is a short period of pure limestone deposition, fol- 

 lowed by a period characterized by conglomerates of the mixed 

 type, certain of whose pebbles contain the same fossils as the 

 cement (Ophileta complanata), proving that the conglomerate 

 is truly intraformational in character. / time sees the close of 

 the period characterized by 0. complanata. Uplift and erosion 



