MUSEUM OF COMPAKATIVE ZOOLOGY. 



115 



long-disputed quostiun of the relative age of the traps and eastern sand- 

 stones of Lake Superior. The dip of the nielaphyr is about the same as 

 that of the sandstone. Immediately above this thin lava sheet, a con- 

 glomerate comes in, forming the fifth fiilL The base of this conglom- 

 erate is composed of a fine-grained detritus formed from the melaphyr 

 and trachyte, and holds numerous pebbles of the melaphyr, as well as 

 of the other rocks (531, 532, 533, 534, 535, 536). Immediately over- 

 lying this conglomerate is another melaphyr flow, and we have here on 

 the eastern side a repetition of the same alternate bands of melaphyr 

 and sandstone that occur on the western side. 



It is to be remembered that Mr. Agassiz, in conjunction with Mr. 

 L. (I. Emerson, the well-known mining engineer of Hancock, and at one 

 time assistant on Prof. Pumpelly's geological survey, found below the 

 Douglass Houghton Falls pebbles of the melaphyr (amygdaloid) in 

 the sandstone; and from this the conclusion was drawn that the sand- 

 stone was younger than the trappcan formation. At the time of our 

 visit to this locality, we had no knowledge of Mr. Agassiz's observa- 

 tions,* except from the general statement of Prof. Pumpelly.t It will 

 be seen that no localities were given by Prof. Pumpclly, although he con- 

 firms Mr. Agassiz's statements. The falls were said by Mr. Agassiz to be 

 located at the junction of the sandstone and trap, while on both sides 

 of the ravine the horizontal sandstone beds were traced up to the falls. 

 Our examination showed that immediately below the falls sandstone 

 and conglomerate exist, dipping N. ib"" W. 25° (504, 505). While the 

 majority of pebbles were of the usual character, one grayish granitoid 

 pebble (50G) containing epidote was obtained. This has suffered the 

 same graphic alteration in Its feldspar that No. 527 has. Much of the 

 feldspar is seen to bo triclinic. Otherwise than its containing more 

 quartz, its characters are in the main like No. 527. The sandstone, at 

 its junction with the overlying trap, is much indurated and altered, and 

 specimens were obtained showing the junction of the two (507, 508, 509, 

 510, 511). As the sandstone underlies tlic trap, it is of necessity the 

 prior-formed rock. Wo suppose that this was the locality at which 

 Messrs. Agassiz and Emerson obtained their specimens of melaphyr in 

 the conglomerate. If so, it is easily enougli explained, for conformably 

 underlying this sandstone is another sheet of melaphyr, then more sand- 

 stone, again more melaphyr, and so on, all conformably underlying one 

 another as much as they do anywhere within the trappean belt, or can 



* Proc. Bost. Soc. Nat. Hist., XI. 214-246. 

 t Geol. of Mich., Part H. p. 3, 



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