PALEOZOIC GROUP. 289 



with these near the summit. In portions of what I have taken to be Riley 

 Beds the ferruginous segregations are very numerous. These are not always 

 commercially valuable, but there are extensive strata of this horizon which 

 in certain localities contain enough iron to be profitably worked. We shall 

 discuss this feature and the distribution of such " bonanza areas" in another 

 place. (See Part II.) The cause of such occurrences may be readily ex- 

 plained. 



The Mid-Cambrian life of the Riley Epoch has not been distinctly outlined 

 for this region. Walcott thinks it absent from our rocks, but I have taken 

 forms closely allied to Lingulella ccelata, Hall (sp.), Lingulella ella, H. and W., 

 Hyolithes americanus, Billings, and Orthisf highlandensis, Walcott, besides 

 Eocystites? and undetermined sponges and fucoids. These do not necessa- 

 rily indicate a middle Cambrian fauna, but they do not disprove it; for the 

 known species all occur elsewhere in Walcott's Middle Cambrian, although 

 not wholly characteristic of this series. There are no known places in the 

 Riley Series where the beds are suitable for the preservation of the Poecillo- 

 poda (including Trilobites), and no such fossils have yet been found. Not far 

 above this, however, in the higher Cambrian Series, Trilobites are very 

 abundant, and they are not Paradoxides nor Olenellus. 



(3) THE KATEMCY (POTSDAM) SERIES (UPPER CAMBRIAN?). 



As the writer now views the matter (provisionally), there is a distinct set of 

 red sandstones in position above the highest beds of the Riley Series, with at 

 least an overlap, if not a dynamic unconformity, at the contact. Yery possi- 

 bly further examination in the field in 1890 may render necessary some 

 changes in localities, as it is by no means certain that a well marked bound- 

 ary exists at the base of the series in all exposures. But assuming such a 

 line, temporarily, at the junction of the chocolate limestones of the Riley 

 series with the rocks usually overlying them in good sections, there will 

 generally be found some stratigraphic record of a changed area of deposition. 



From my present limited knowledge of the life of the Cambrian in Central 

 Texas, I dare only report that a conviction has been growing of its probable 

 transitionary aspect, although some few types may be found in only one of 

 the series. The final separation of the Middle and Upper Cambrian will 

 probably be based upon the horizon of the lowest occurrences of Lingula, 

 Dicellocephalus, etc., and my present opinion is that the boundary here drawn 

 is consistent with such a paleontologic classification of the strata. At any 

 rate, my own observations, stratigraphic and paleontologic, are in harmony 

 with this view. 



We may conveniently adopt three divisions for the Katemcy Series, based 

 s 



