DETAILED GEOLOGY 428 



collections have been made. Cambrian fossils have been identified in an 

 anticlinal fold south of Marathon, but not at the Solitario. The white 

 novaculite, which forms conspicuous ridges in the northern half of the 

 uplift, is the most conspicuous Paleozoic formation, and it is clearly the 

 Caballos novaculite which is possibly of Lower Devonian age. Beneath 

 it and within the novaculite rim in the northern half are the black cherts 

 and silicified shales, which belong to the Maravillas formation of Middle 

 and Uj)per Ordovician age and contain graptolites at Marathon.'^ The 

 (dder blue and gray limestone and black shale are probably the Marathon 

 formation of Lower and Middle Ordovician age. Overlying the novacu- 

 lite and structurally conformable with it is the Tesnus formation, of 

 Pennsylvanian age.* The Tesnus formation is exposed in the south part 

 of the Solitario and in the synclines in the northeast and southwest parts 

 of the novaculite. Plant remains collected 325 feet from the top of the 

 Tesnus formation at Marathon (latitude, 30° oi/o'; longitude, 103° 19') 

 were identified by Mr. David White as probably of Upper Pottsville age, 

 to l)e correlated Math the base of the Magdalena group of New Mexico and 

 with either the Strawn or Bend formations of Avest central Texas. Uplift 

 and erosion everywhere followed the deposition of these and accompany- 

 ing formations. 



Pennsylvanian or Permian (?) limestones are exposed on either side 

 of the wagon road in the north end of the Solitario, between the basal 

 Cretaceous conglomerate and hills of igneous rock. The hills seem to 

 re|)rescnt an intrusion which came up along the fault separating these 

 Pnie^tcnes from those of Ordovician age. The limestone is bright yellow 

 ill color, the appearance being similar to that of the Permian limestone 

 ill Shackelford County. It contains crinoids and other poorly preserved 

 fossils, which are of Upper Paleozoic age. The only Pennsylvanian lime- 

 stone with which it can be correlated is the Dimple at Marathon, but 

 tliere are many Permian limestones. 



liower Cretaceous sedimentation followed a period of orogeny and ero- 

 sion. The basal Trinity conglomerate, 100 feet or more in thickness, 

 consists of well rounded pebl)les. The absence of lithologic breaks in tlie 

 overlying limestone series and the thinness of the l)asal coiiiilomerate 



■ Dr. Kudolf Kuedemann identified tlie graptolites as of Trenton Normanskill ape. 

 Collections from the Viola limestone in the Criner Hills, Oklahoma, indicate a slightly 

 younger Trenton horizon, 



* 'J'his formation was measured along San Francisco Creek parallel to tlie Southern 

 I'acitic Itailroad east of Marathon and found to I)e 7, .500 feet thick, subject to duplica- 

 tions, but only two. apparently minor faults, were observed. Baker and liowman meas- 

 ured the thickness as :!,M70 feet. The overlying Dimple formation was deterniincd to be 

 S.S-J feet thick. 



XXX--P.ILL. r.iAH,. Soc. A.M., VuL. A-2, IICJO 



