1916] The Ottawa Naturalist. 29 



A PRELIMINARY PAPER ON THE ORIGIN AND CLASSI- 

 FICATION OF INTRAFORMATIONAL CON- 

 GLOMERATES AND BRECCIAS. 



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



Introduction. 



The term intraformational in contradistinction to inter- 

 formational was first proposed by Walcott (1) in 1894. He 

 writes: "An intraformational conglomerate is one formed within 

 a geologic formation of material derived from and deposited 

 within that formation." In the same paper he remarks upon 

 the importance of determining the time element or sequence of 

 events in the formation of a sedimentary or clastic rock, by a 

 study of the shapes and textures of its constituents. Thus, in 

 his introduction he writes (p. 91): "Usually the presence of a 

 conglomerate in a stratigraphic series of rocks is a matter of 

 considerable importance to the geologist. He naturally infers 

 the presence of a break in the continuity of sedimentation; an 

 orographic movement of greater of less extent; erosion of pre- 

 existing formation." In other words the term conglomerate 

 by its definition conveys to the mind of the stratigrapher a 

 great difference between the ages of the pebbles and the 

 cement. It is proposed to show in this paper that there is often 

 a nice distinction between the ages of the constituents in most 

 conglomerates and in intraformational conglomerates in parti- 

 cular. It is true that we arrive at a knowledge of the sequence of 

 the events which have taken place in the formation of any given 

 clastic by describing the texture and shape of its constituents, 

 but the writer believes that the tendency has been too strong 

 among students of the sedimentary rocks to express their find- 

 ings in purely textural and structural terms without special 

 thought as to their history and origin. Thus, any rock, be it 

 limestone or otherwise, which is formed of coarse and appar- 

 ently water-worn materials, is dubbed a conglomerate, and 

 its natural history, even if recognized, is lightly passed over in 

 its classification. 



It is not proposed in this paper to attempt a classification 

 of all conglomerates on such a basis as outlined above. A 

 study of certain Paleozoic limestone conglomerates, and espe- 

 cially of certain structural and textural phenomena as exhibited 

 in the limestone formations at Trenton Chasm, Chambers- 



