THE CANTW ELL FORMATION 127 



The Cantwell as indicated by its plant remains and character 

 is of Eocene age and corresponds in whole or in part to the Kenai 

 formation, widely distributed in isolated areas through Alaska. 

 This correspondence, however, should be regarded as a general one, 

 without implication of exact time coincidence or precise analogy 

 of formations; for the Cantwell formation and the Kenai, being 

 throughout dominantly continental deposits, cannot be expected to 

 display the degree of equivalence normal to marine deposits. 



Origin^ — The character of the sediments composing the Cant- 

 well formation signifies fluviatile continental deposition. The 

 extensive development, number, and thickness of the conglomerate 

 beds and the heterogeneous character of this rock indicate a source 

 of supply under violent degradation, a short transport, and dis- 

 tribution by rushing waters competent to spread material of such 

 coarseness. The presence, moreover, between the conglomerate 

 members of carbonaceous mud rocks, carrying well-preserved plant 

 remains in abundance and variety, implies areas of quiet deposition, 

 such as swamps and small lakes, which alternately superseded, and 

 in turn were transgressed by, zones of depositional activity. These 

 conditions are afforded by voluminous streams emerging from a 

 mountainous region on to a piedmont slope, intermontane valley, 

 or shallow sea. 



It is difficult with present information to decide whether the 

 Cantwell was laid down as an interior continental deposit or upon 

 the inland margin of a delta built out from a coast range of moun- 

 tains. The apparent absence of deposits that might be attributed 

 to the seaward portion of such a delta, the predominance of con- 

 glomerate over finer elastics, and topographic considerations incline 

 the writer to favor the first explanation; although on this basis, for 

 the preservation of the sediments from subsequent complete ero- 

 sion, it must be assumed that downward warping in front of the 

 mountain axis succeeded their deposition. That a compressive 



' The interpretation of the origin of the Cantwell formation has been facilitated 

 by a study of the contributions of Barrell on sedimentation, especially those appearing 

 in Jour. GeoL, XIV (1906), 316-56, 430-57, 524-68; XVI (1908), 159-90, 255-95, 

 363-84; Bull. Geol. Soc. Ainer., XX (1909), 620; XXIII (1912), 377-46; and.Amer. 

 Jour. Sci., XXXVI (1913), 429-72; XXXVII (1914), 87-109, 225-53. See also 

 Mansfield, Jour. Geol., XV (1907), 550-55. 



