318 



in moderately thin sections, while the included pellets are 

 very finely granular in texture and of darker colour than the 

 matrix. Most of them are sharply defined from the matrix 

 and are destitute of any distinct concretionary shells. A few 

 exhibit a very thin, dark-coloured exterior ring, and a more 

 translucent and equally thin circle immediately below it, with 

 the usual dark, granular texture below the latter. In some 

 the outer circle forms the semitransparent ring, and, the 

 inner, the darker. Most have no nucleus, while others have 

 either transparent centres or darker than the intermediate 

 zone. 



The brecciation (pi. xix.) is more developed in this 

 locality than in the beds further south. Angular fragments, 

 identical in texture with the groundmass, although usually of 

 a lighter colour when viewed macroscopically, are numerous 

 and of all sizes up to three inches in length. In a few 

 instances, noted, they were longer than this, in the form of 

 flat layers, or slightly curved, from a quarter of an inch to 

 half an inch in thickness. A curious feature is present in 

 that the larger brecciated fragments sometimes carry 

 inclusions of smaller angular fragments within them, which 

 also contain the oolitic-like granules. When the edges are 

 straight and sharp the fracture has passed through some of 

 the granules, giving evidence of subsequent movements. In 

 other cases the dark-coloured ferruginous cement has united 

 a number of the spheroidal bodies together and forms a sharp, 

 dark line at the boundary^ making a scalloped edge as it 

 passes around the projecting spheres on the margin. While 

 there is generally a rough parallelism in the way in which the 

 fragments lie in the bed, there are instances in which they 

 take a vertical position answering to the form that Hahn has 

 called ''edge-wise conglomerates." 



As in the case of the Burra section, some of the limestone 

 at the Depot Creek forms a wavy and concentric structure. 

 Individual examples, when rubbed down, show a certain 

 resemblance to nodules of the Stromatoporoidea, as hand 

 specimens, but on examination of thin sections of the rock 

 under the microscope they show no relationship to such 

 organisms. 



General Remarks on Certain Rock Structures of the 

 Limestone that forms the Brighton Horizon in the 

 Lower Cambrian. 

 1. The outcrops that come under review in this paper 

 extend over a lineal distance of 250 miles. There is a general 

 similarity of rock features, both microscopically and macro- 

 scopically, at the same horizons throughout this area, which 



