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University of California. 



[Vol. 2. 



age and have had the same life history since they were formed. 

 Together they have been subjected to mountain building forces, 

 being irregularly folded and faulted, and dyke rock injected into 

 the fissures; they have been metamorphosed to the same extent; 

 and they both have the abundant irregular veinlets of white quartz 

 and white calcite, indicating general fracturing. So far as appear- 

 ances go they are much older than any other formation yet found 

 on the Isthmus. 



While examining the green eruptive I was impressed by a 

 marked resemblance in many particulars to a diabasic formation of 

 Jura-Triassic age in northern California, and thought the entire 

 complex including the limestone might be of Jurassic age. The 

 fossils in the limestone seemed not of types common to Carbon- 

 iferous or older faunas, but appeared to be of a somewhat newer 

 facies. For reasons which will appear later, I had to place this 

 formation earlier than the late Cretaceous and hit upon the Jurassic 

 as the age best indicated by the evidence. Lately, upon becoming 

 acquainted with the characteristics of the Franciscan series of the 

 Coast Range region of California (thought by Lawson to belong 

 somewhere in the interval between the recognized typical 

 Jurassic and the typical Cretaceous formations), I have recog- 

 nized the fact that the Azuero-Torio complex and the Fran- 

 ciscan series have had an identical life history since their forma- 

 tion; that is, they have suffered the same orographic disturbances, 

 alterations of a like degree and like character, and are separated 

 from newer formations of known age by non- conformities of equal 

 value. 



Now, ordinarily lithologic resemblances are too uncertain a 

 means of correlation in such widely separated districts as the 

 Isthmus of Panama and California, but as suggestive of what cor- 

 relations will finally be made, let us assume that the oldest series 

 on the Peninsula of Azuero represents the same late Jurassic or 

 early Cretaceous sediments and eruptives as the Franciscan of 

 California, that the alteration of one was part of the same metamor- 

 phic action as that of the other, and that the land area following 

 the deposition of the Torio limestone and injection of diorite in the 

 Isthmian region, represents the same epoch of the early Cretaceous 



