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REVIEWS 



the more exact scheme of analysis described by Trager, however, was 

 not resorted to. Depths from the surface are plotted as ordinates in 

 ten-foot units and the composition in percentage of argillaceous, arena- 

 ceous, flinty, and calcareous sediments, as determined from the log 

 samples, are the abscissae; the diagram thus constructed is essentially 

 a graphic columnar section. Correlation is based on the relative increase 

 or decrease of one type of sediment, rather than on the absolute per- 

 centage composition of the bed in question. A mere glance at the plate 

 given serves best to illustrate the method used. Flinty sediments are 

 taken to be equivalents of calcareous deposits, since the conditions under 

 which they originally formed are similar. 



Such ratios established a generalized sequence for the counties of 

 Comanche and Palo Pinto (and probably also Eastland and Stephens, 

 the intervening counties). This sequence follows: 



Pennsylvanian 



Mississippian 



Strawn formation 



True "Upper Smithwick" shale 



"Smithwick lime" 



"Lower Smithwick shale" of the Ranger 



field 

 "Black lime" of the Ranger field 

 A succession of limestones and sandy 



limestones, hitherto unnamed 



/ Lower Bend limestone 

 \ Lower Bend shale 



' =True Smithwick 

 shale 



: True Marble 

 Falls limestone 



Unconformity 

 Ordovician — Ellenburger limestone 



The entire Pennsylvanian and Mississippian (including the lower part 

 of the Strawn) has an average thickness of i,ioo feet. 



No marked unconformities are reported above that which separates 

 the Ordovician and Mississippian, though eleven disconformities of 

 varying importance, not indicated above, are recognized. Several 

 are intraformational. In the case of the disconformities, glauconite and 

 phosphate nodules in some cases mark the plane of separation. These 

 glauconite grains are coarser and less rounded than those of the thick 

 greensands of other horizons and resemble more closely those of the 

 New Jersey Cretaceous. The occurrence of sulphides at the horizons 

 marking ' akinetic" surfaces of maximum base-leveling is another note- 

 worthy feature. 



Many other interesting facts are discussed, and points of consider- 

 able theoretical significance are brought forward — such as the source of 



