200 BULLETIN OF THE 



rock at the localities, rather than by difference of other conditions. 

 Along the portage past this foil are several small exposures of granite 

 ledge, the only ones that were seen near the river, apart from its bed or 

 banks. 



The granite of the three ledge-formed falls, as well as that of Ktaadn, 

 beyond any other that I have elsewhere seen, is free from veins and 

 dikes. In fact the only instances observed of either in the whole 

 region were a quartzose vein, an inch wide, that ran through a block 

 twenty feet in length, evidently torn from the rock on which it rested at 

 the fourth fall ; and a small trap dike, four inches wide, that traversed 

 a nearly buried erratic bowlder lying on the portage at the fifth fall. 



Another circumstance common to the granite of the several localities 

 is, that at the falls only is it visible. Above and below each fall the rock 

 so suddenly and entirely disappears, that over the spaces between the 

 falls granite in place could nowhere be discovered. It would seem, then, 

 that at the thii'd, fourth, and fifth falls a ridge of granite in each case 

 cuts the river bottom transvei'sely, damming the stream and obliging it in 

 its course seaward to tumble in a fall over the lower slope of the ridge. 

 The underlying fixed rock which intervenes between the granite ridges 

 is so hidden by drift deposits that nothing can be asserted positively 

 concerning its nature. One would naturally suppose it to be granite ; 

 but without attaching much importance to the marked difference between 

 the rock of the upper fall and that of the two next below, there are other 

 considerations, to be noticed presentl}', which suggest a doubt whether 

 the three ridges that occasion the three ledge-formed falls have any lat- 

 eral connection below the drift, and the question whether they may not 

 be distinct ridges of intrusive rock, thrust up through strata from a com- 

 mon source beneath. 



The theory that the district south of Ktaadn is part of a continuous 

 granite region, is a hasty generalization from insufficient data, origi- 

 nally made by Dr. Jackson. Prof. Hitchcock, in his survey, which was 

 discontinued at the close of its second year, made no personal examina- 

 tion of the Penobscot valley between Chesuncook Lake and Grand 

 Falls. He therefore naturally adopted in the construction of his geo- 

 logical map Dr. Jackson's view of that district, supplemented by some tes- 

 timony of one of his own assistants. The map was of course intended to 

 be provisional only, and, had the survey been continued, would probably 

 have been superseded by others. All the basis that exists for belief in a 

 wide granite area south of Ktaadn is found in a few passages of Jack- 

 son's and Hitchcock's Reports. They can here be presented in small 

 compass. 



