526 GEORGE DAVIS LOUDERBACK 



lower series, rather arkose, but, while some of the beds may be quite 

 hard, the induration, in general, has been much less than in the 

 lower sandstones. On a surface of fracture the grains stand out in 

 relief and the clastic character is always readily recognizable. The 

 excessive fracturing and crushing found in the lower sandstones is 

 absent, and the beds maintain their individuality and distinctness 

 for considerable distances, although the thin beds, being lens-like in 

 nature, are less persistent than the structures — folds, etc. — which 

 latter may be traced for many miles. With the absence of the 

 abundant fracturing and of the cementation characteristic of the 

 lower series may be associated the practical non-existence of quartz 

 veins, veinlets, or masses in the upper group. Small calcite stringers 

 are sometimes found, but only rarely a slight local development of 

 secondary silicious material in small veinlets. Phases where the 

 individual grains are flattened into an incipient schistose structure, 

 and actual development of recrystallized facies, were nowhere 

 observed. 



Conglomerates. — Conglomerates are rather more common than 

 in the lower series, and are quite indurated and show faulted pebbles. 

 With the exception of showing less the effects of squeezing and 

 crushing, they have very much the general appearance of the con- 

 glomerates of the lower series. While very largely made up of chert 

 pebbles, they frequently carry pebbles of some of the other rocks 

 which occur in the lower series, as will be explained later. 



The conglomerates occur chiefly in the lower part of the upper 

 group. It is possible that one may be found that marks the begin- 

 ning of the Horsetown epoch of deposition. However, no attempt 

 was made to discover such a stratigraphic boundary for those beds. 

 Of great interest in determining the relationships of the two major 

 divisions is the heavy basal conglomerate of the upper group — over 

 a thousand feet thick — which in the vicinity of Myrtle Creek can be 

 traced for probably twenty miles or more. This will be more fully 

 described later on. 



THICKNESS OF THE SEDIMENTS 

 The upper division. — The thickness of the upper division is per- 

 haps most simply and satisfactorily measured in the vicinity of 

 Myrtle Creek. It is here folded into a syncline which may be traced 



