312 C. W. HAYES — GEOLOGY OF NICARAGUA CANAL ROUTE 



verge slightly toward the northwest, indicating a pitch of the anticline 

 in that direction. 



The exposures of the Brito formation are so infrequent and the dips 

 are so variable that no satisfactory measure of the thickness of the forma- 

 tion can be obtained. Taking the observed dips between the Pacific 

 coast and the lake shore, the thickness exposed is estimated at upward 

 of 10,000 feet. This, of course, is not the total thickness of the forma- 

 tion, since the bottom is not exposed at the axis of the anticline ; also, 

 the formation has undoubtedly suffered an unknown but considerable 

 diminution in thickness by erosion, and there are no data for determin- 

 ing the thickness of strata which have been removed from the highest 

 beds now observed. 



Age of the formation. — The greater part of the Brito formation is apj^ar- 

 ently barren of organic remains. The only locations at which fossils 

 have been found are on or near the Pacific coast. This, however, may 

 be due to the fact that the rock exposures are not elsewhere of such a 

 character as to facilitate the discovery of fossils, and the latter may possi- 

 bly be more generally distributed than present knowledge would indicate. 

 The fossils are confined almost wholly to the limestones and marly beds. 

 They consist of corals, molluscan and foraminiferal remains. The latter 

 are especially abundant. The rather meager collections have been sub- 

 mitted to Dr Dall for determination. He pronounces them Oligocene, 

 and probably identical with the foraminiferal beds described by Hill from 

 the Caribbean coast at Panama. One of the most abundant forms is a 

 small numulite, Orbitoides, probably forbesei, which is characteristic of 

 the lower Oligocene. The molluscan remains were collected on the Pacific 

 coast, about 75 miles northwest of Brito, in what was supposed to be a 

 higher portion of the same formation. Dr Dall states that these have the 

 upper Oligocene aspect, though there are not enough of them to be con- 

 clusive. He thus confirms the view entertained in the field, that suc- 

 cessively higher beds in the Brito formation are exposed along the coast 

 toward the northwest. 



In addition to the fossils on which is based the above conclusion con- 

 cerning the age of the Brito formation, it also contains rather abundant 

 plant remains. They are in the form of driftwood and coal, but as yet no 

 remains sufficiently well preserved for identification have been discovered. 



Associated with the coarser sandstones are numerous blocks of wood, 

 whose rounded forms suggest that they are fragments of drift which were 

 incorporated with the sand and gravel while it was accumulating. In 

 some cases they still contain a large proportion of their original carbon, 

 and in others this has been more or less perfectly replaced by silica or 

 iron pyrites. The coal occurs associated with the finer sediments, and, 



