Evidences which have been previously advanced relative to the age of the Ouachita orogeny are reviewed and discussed in the first part of the paper. The conclusion is drawn that there is very little evidence in support of a Pennsylvanian age that will withstand a close examination. The chief evidence cited is the presence of chert-pebble conglomerates in the lower Pennsylvanian formations of the eastern part of the Lehigh syncline and northward. The supposition that these chert pebbles originated in the Talihina "chert" formation of Black Knob Ridge (which borders the syncline on the east) is shown to be probably incorrect. In view of the evidence presented, the buried southeastern extension of the Arbuckle Mountains is thought to be a more probable source.

Additional evidence relative to the age of the exposed Ouachita Mountains is found in the joint systems of the central and northern Oklahoma plains. This evidence leaves no doubt whatever that an important part of the more intense phases of the Ouachita orogeny occurred after early (Oklahoma) Permian time, and there seems to be a strong probability that all of it occurred then. One of the chief joint systems of central Oklahoma radiates fan-like from the front of the Ouachita Mountain arc, and apparently decreases in "intensity" with distance from these mountains. The short faults of the so-called "en echelon fault belts" in central Oklahoma may be correlated very closely in strike with the joints of the radiating system referred to, and are thus, from the standpoint of origin, connec ed with these mountains more closely than before. Doubts are expressed as to the common occurrence of true en echelon fault belts in Oklahoma.