284 CENTRAL MINERAL REGION OF TEXAS. 



sea to the eastward, with a western shore line of undetermined contour well 

 beyond the middle of Llano County, at any rate. The indications are, how- 

 ever, that a large part of the old Archaean land areas were still above the 

 sea. The shore line may have encroached upon these earlier highlands in 

 part, but no evidence has yet been obtained of any Cambrian depositions 

 west of the boundary line between Mason and Menard counties. Walcott 

 believes that his middle and lower series of the Cambrian System are absent 

 from this area, but, he remarks : 



The orographic movement that brought the Grand Canyon, Llano, and Keweenawan 

 formations above sea level probably extended all along the central line of the continent, 

 leaving the Atlantic area and the Great Basin of Utah, Nevada, Arizona, etc., areas of 

 deposition during the existence of the Paradoxides (Lower Cambrian) fauna, and probably 

 during the existence of the Middle Cambrian fauna, a break on the north or south permitting 

 the latter fauna to pass into the western basin now covered by a portion of the Rocky Moun- 

 tains.* 



Without discussing other views of this author concerning which our evi- 

 dence is not yet complete, it may be said that the above quotation is largely 

 verified by my own observations in Central Texas; but for reasons which are 

 to follow I can not agree with him that our area is deficient in representa- 

 tives of the earlier Cambrian strata. 



There is one remarkable stratigraphic feature, a series of topographic relief 

 forms, which has been so much a puzzle that at times it has seemed well nigh 

 inexplicable. This is, however, but the strongest of many warnings which 

 this district presents against reporting hasty conclusions. Very gradually, 

 after rejecting numerous hypotheses which were consistent with one or other 

 of the facts, the writer has been enabled to get a clew to the history. Smooth- 

 ing Iron Mountain and some of the neighboring elevations, certain of the 

 peaks of the irregular group of the King Mountains, Sharp Mountain, Hick- 

 ory Mountain, Town and Fox Mountains, Sandy Mountain, the eastern end 

 of Packsaddle Mountain, and the Little Mountain near the Llano Falls, with 

 probably a number of other eminences, are all capped by beds of massive 

 sandstone or quartzite, sometimes underlaid by a coarse conglomerate of 

 rounded white quartz pebbles in a red granular sandy or feldspathic matrix. 

 Similar occurrences have been noted elsewhere, but subsequent upheavals 

 have so much modified the original unconformity that it is often very difficult 

 to detect the real structure at the contacts. But in many instances the field 

 notes give hints of unconformity which can be readily explained by the aid 

 of this section. 



Putting together the various items, the following stratigraphic summary is 

 found to be in harmony with them all: 



*Bulletin United States Geological Survey, No. 30, 1886, page 58. 



