Hershey.] 



Isthmus of Panama. 



241 



as the land area indicated by a non -conformity between the Fran- 

 ciscan and Knoxville of California. We will provisionally adopt 

 this as a basis upon which to build up our Isthmian column of 

 formations and will see how we will come out at the top or when 

 we reach a formation whose age has been fixed by study of its 

 fossils. 



The Montijo Conglomerate. — On the eastern shore of the Gulf 

 of Montijo, opposite the island of Cebaco, about one mile north of 

 the Torio River, there is a great formation, hundreds of feet thick, 

 of fine conglomerate, hard and gray in color. It is well stratified 

 and dips usually at a high angle. There are occasional fossils, but, 

 I fear, too imperfect for specific identification. Coarse conglomera- 

 ate and fine sandstone are both rare. The outcrop in the sea has 

 a reddish tint. 



The conglomerate formation is newer than the Torio limestone 

 and is distinctly seen to rest on it. Between them is an important 

 non-conformity. The green eruptive and limestone were contorted, 

 faulted, the fissures filled with diorite, the white veinlets formed a 

 larger part of the metamorphism accomplished, and the whole com- 

 plex reduced by erosion from a mountain mass to comparatively 

 low ground before the Montijo conglomerate was deposited on the 

 submerged borders of the old land. This will rank with the great 

 non-conformities in the United States. It appears to be of the same 

 value as that separating the Franciscan and Knoxville series in 

 California, and we will provisionally correlate the Montijo conglom- 

 erate with the latter formation of known early Cretaceous age. 



The Montijo conglomerate is separated from the next newer 

 formation by a non-conformity represented by a tilting of the for- 

 mation and sub-aerial erosion. This was not nearly so long as the 

 preceding erosion interval and appears to be of the same value as 

 that separating the Knoxville and Chico in the Coast Range region 

 of California. We shall, therefore, expect to find some evidence of 

 the Upper Cretaceous age of the succeeding formation. 



Tlic Santiago Formation. — At the town of Santiago de Veraguas, 

 where first discriminated, this is made up of thick layers of non- 

 laminated shale of a dull greenish gray color and a peculiar breccia 

 and breccia-conglomerate. The latter are characteristic of this 



