CAMBRIAN AND LOWER ORDOVICIAN. 79 



This section was measured in, dipping beds and the total thickness as stated is beheved 

 to be somewhat short of the actual thickness. The section is of value, however, as indicating 

 the succession. 



Certain characteristics of these formations deserve a more detailed description. 



A wide diversity exists in the basal members. Locally they are fine-grained, cleanly washed 

 sands; elsewhere they are coarse conglomerates with pebbles ranging from 6 to 8 inches in 

 diameter. A marked relation was noted between the underlying pre-Cambrian and the basal 

 layer. Certain coarse granites rich in pink feldspar have produced a pinkish-white conglom- 

 erate, in which the rounded quartz grains average a quarter of an inch in diameter and which 

 contains numerous angular fragments of feldspar. A clean white cement consisting of small 

 quartz grains and feldspar fragments with calcium carbonate binds the whole. In another 

 place a coarser conglomerate stained red contains subangular quartz fragments as large as half 

 an inch and feldspar fragments an inch long. A fine-grained quartz cement which included, 

 particles of iron oxide was the matrix. In another place a coarse sandstone containing 1 to 2 

 inch fragments of hematite makes up the basal layer, the iron having been derived from the 

 underlying schists probably in the form of magnetite and later altered to hematite. In yet 

 another place where the underlying formation is rich in pegmatite dikes, large angular masses 

 of quartz are abundant in the lower beds. Here and there the lower member, where resting 

 on a coarse-grained granite surface, is a granite arkose. 



In different localities the conditions of sedimentation undoubtedly varied, and this variation 

 is expressed in the inadequacy of a hard and fast line between the Hickory sandstone and the 

 Cap Mountain formation. The sandstones become gradually more limy, until the beds are 

 predominantly limestone. In drawing a boundary line between two such formations, it is 

 often difficult to decide upon a satisfactory line, though taken as a whole the two sets of beds 

 fully justify such a separation. 



The distribution of glauconite in the Cambrian strata is interesting. Beginning in the Cap 

 Mountain formation, it appears in scattered grains in the pure limestones and reaches its greatest 

 development in cross-bedded sandstones, the top of which is used as the boundary between 

 the Cap Mountain formation and the Wilberns formation. Above this sand the glauconitic 

 material gradually disappears. Though where observed in limestones the glauconitic grains 

 exist essentially as such, in the sandstones the material" is more likely to form the matrix in 

 which the well-rounded clean quartz grains are embedded. 



UPPER CAMBRIAN AND LOWER ORDOVICIAN. 



The rocks overlying the Wilberns formation are of late Cambrian and early Ordovician age 

 and have not been subdivided. They have been given the local name EUenburger limestone. 

 They are regarded by Ulrich as equivalent to a small portion of the rocks of similar age in the 

 Missouri section and also to the lower part of the Arbuckle limestone of Oklahoma. In the 

 greater number of places where the base of the Ellenburger Hmestone was observed, it is appar- 

 ently conformable with the Wilbems formation. Many observations were made where no 

 Unconformity could be detected and where an apparent transition between the two formations 

 could be followed. It must be noted, however, that the basal beds of the EUenburger limestone 

 vary in texture and appearance, and that this phenomenon is in itself a suggestion of uncon- 

 formity. Any decision, therefore, mtist for the present remain tentative. 



At the top of the Ellenburger limestone there is usually, though not always, a conglomerate 

 limestone bed, succeeded by the lowest portion of the Peimsylvanian (upper Carboniferous). 

 The Upper surface of the Ordovician on Doublehom Creek just south of the road crossing half 

 a mile north of the mouth of Cordova Creek gives an excellent example of the pre-Carboniferous 

 surficial conditions. 



The upper 25 feet of the Ordovician is composed of large angular blocks, very irregularly 

 disposed, reveaUng a condition of peculiar surface breakage prior to submergence beneath the 



