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202 COAL FIELDS OF THE COLORADO RIVER. 



which the sediments composing the Carboniferous strata were derived. Rest- 

 ing unconformably upon these rocks is a limestone, which is also unconform- 

 able with the true Carboniferous. These beds appear as a narrow strip, sep- 

 arating the Carboniferous from the Silurian, and consist almost entirely of 

 crystalline limestone with beds of shale. The beds of the Lower Carbonifer- 

 ous series were formed mostly in rather deep water off the shore of an old 

 Silurian land area, and the beds of the sea shore may yet be seen in the form of 

 shales, and rarely conglomerates in the bays and on the headlands of the old 

 shore line, which may be plainly traced. The dip of the beds is somewhat 

 variable, but the average is gentle, from 1 to 2 degrees northwest. In one 

 place the dip is 20 degrees in the same direction. There are small anticlin- 

 als and synclinals much more numerous than in the Upper Carboniferous, 

 where they are very rare. Unless carefully mapped and studied over a con- 

 siderable area, this formation might be overlooked and classed as a portion of 

 the Upper Carboniferous. The fossils resemble those found in the true Car- 

 boniferous, though upon closer study some will undoubtedly be found to be 

 quite different. One specimen of Goniatites has been pronounced by Prof. 

 Alpheus Hyatt to be a distinctive Lower Carboniferous form. 



The deceptive resemblance of fossils would at first lead to a decision that 

 these beds are a part of the Upper Carboniferous, and this deception is in- 

 creased when an actual contact occurs between the strata of the two forma- 

 tions. At two places east of San Saba the limestone seems to dip conforma- 

 bly beneath the sandstones. In both these places the dip of the strata of 

 each series is the same. It is only when we see the section as a whole that 

 the true relation of the two series is discovered. The San Saba River, from 

 just above its mouth nearly to the mouth of Richland Creek, is the dividing 

 line between the Upper and Lower Carboniferous, and this line of division 

 is continued westward up the valley of Richland Creek. On the north side 

 of this line is the true Upper Carboniferous, consisting at this place of a 

 great thickness of sandstone. South of this line is the Lower Carboniferous, 

 composed in this region entirely of limestone and limy shales. As a person 

 crosses the region for the first time there are three possible explanations of 

 such a relation of beds. The first is that the limestones and sandstones are 

 interstratified ; but this is quickly disproved, since in the sandstone areas 

 there are no limestones, and in the limestone regions no sandstones. This 

 and abundant other field evidence proves that the limestone is beneath the 

 sandstone; and then the problem is narrowed down to two possible solu- 

 tions — the two series are either conformable or unconformable. There are 

 two proofs that they are not conformable. The dip of the limestone averages 

 at least two hundred feet to the mile, and with such a dip any bed of lime- 

 stone, as for instance the bed on the Colorado below Red Bluff, would soon 



