1916] The Ottawa Naturalist. 33 



is proposed to designate the larger fragments, pebbles or allied 

 forms which are easily distinguished from the ground mass or 

 cementing material. They, the phenoclasts, may be of several 

 orders of size. The term is convenient, as it is not always cor- 

 rect to refer to the major constituents of a conglomerate as 

 pebbles, or even brecciated fragments. For instance, in the 

 edgewise "conglomerates," the "pebbles" and cement are apt 

 to be formed from the same material; also the shape of the 

 "pebbles" is hardly pebble-like, neither are the "pebbles" true, 

 brecciated fragments. Also, in certain types to be described 

 later, the bioglomerates, the phenoclasts are obviously neither 

 pebbles nor angular material. Their outline is as peculiar and 

 distinct as is their origin. Thus we find all variations, from 

 sand-like particles to pebbles and breccias, and all of them con- 

 spicuously distinct from the cement or ground mass. 



Classification. 



(See table on page 35.) The stratigrapher is primarily in- 

 terested in the " sequence of events," as exhibited by the relative 

 position of , and the structures and fossils within, the formations 

 which he studies in the field. He must observe texture and 

 structure as well as fossils in short, he should be lithologist 

 and structural geologist as well as paleontologist. What little 

 the present day stratigrapher knows regarding the texture of 

 the sedimentary rocks, he has acquired with the methods of 

 the petrologist, methods largely developed for the investigation 

 of the igneous or crystalline rocks. The petrographer studies 

 his thin sections and classifies his specimens according to their 

 macroscopic and microscopic textures and mineral contents ; 

 the resulting data, together with the structural details and 

 occurrence of the rocks in the field, are used by the petrologist 

 to build his classification of the igneous rocks and to promote 

 his theories as to their history and origin. Thus, studies in 

 " paragenesis " and "order of crystallization" within veins and 

 hypothetical rock melts have resulted in our present knowledge, 

 through facts and hypothesis, regarding the main, great divi- 

 sion of the rocks which form the earth's crust. Microscopic in- 

 vestigation of the sedimentaries, and especially of the limestones, 

 has not appealed to the petrographer. The supposed lack of 

 variation in texture, and more or less homogeneous mineral 

 composition, has failed to raise the same amount of interest 

 in their classification and origin as in the igneous rocks. Even 

 granting the fact that with the limestones are associated, in 

 many cases, the relics of past floras and faunas, which should 

 stimulate investigation as to the history of the rock's formation, 



