58 The Ottawa Naturalist. [Aug. -Sept. 



Cambrian genera showing enlargements of the third segment, 

 includes one species (idahoensis Walcott) (a) characterized by 

 the presence of a long median spine on the fifth segment, and 

 one species (typicalis Walcott) (b) in which the median spine 

 adorns the eighth segment. This enlargement of certain seg- 

 ments is comparatively rare among the trilobites, and its fur- 

 ther study should yield results of morphologic value. The 

 foregoing can only be considered as a resume of some of the 

 facts which may contribute "to the observational basis of the 

 ultimate discussion." 



A PRELIMINARY PAPER ON THE ORIGIN AND CLASSI- 

 FICATION OF INTRAFORMATIONAL CON- 

 GLOMERATES AND BRECCIAS. 



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



(Continued f.oni page 52.) 



Limestone Conglomerates. 

 Intraformational conglomerates have been described which 

 are more nearly related to conglomerates in the ordinary sense 

 than those hereto+ore discussed. The phenoclasts (true pebbles 

 in this case) of these conglomerates are usually of several orders, 

 of size, and all but the largest are water-worn, i.e., derived, by 

 transportation and attrition, from indurated, angular material. 

 The pebbles contain the same fossils as are found in the cement- 

 ing material or ground mass, and thus the conglomerate is 

 proved to be truly intraformational in time. Such conglomerates 

 are of manifold occurrence. Walcott (op. cit. p. 34) describes 

 one from a locality below Schodack Landing, Rensselaer County, 

 N.Y. He writes: "It (the conglomerate) shows that the lime- 

 stone pebbles, boulders and brecciated fragments were formed 

 from a calcareous sediment sufficiently consolidated to be broken 

 up and more or less rounded by attrition, and these collected 

 to form a bed of conglomerates, the matrix of which is usually 

 calcareous." Sometimes these glomerates are very coarse, and 

 contain phenoclasts the size of boulders (two to four feet in 

 diameter). Walcott describes such conglomerates from east- 

 ern Pennsylvania, and others from Tennessee, in Cook, Sevier 

 and Blount counties. In one portion of the Cictico conglom- 

 erates, he states (op. cit. p. 38), some of the boulders reach 



(.n) Smithsonian Misc. Coll., vol. S3, No. 2, 1908, pi. 3. 



(b) Canadian Alpine Jotim. vol. 1, 1908, pi. opp. p. 248, fig. 1. 



