422 THE CANADIAN NATURALIST. [Vol. X. 



per cent, of magnesia, and probably representing the so-called 

 Calciferous sandroek, which is really an impure dolomite. As 

 seen along the railway, these beds have at first a very gentle 

 dip to the northward, which soon grows steeper until, where 

 lost sight of, a few hundred feet from the wall of gneiss, they 

 dip towards it with an angle of about sixty degrees to the 

 northwest. The almost constant eastward dip of the paleozoic 

 strata on the east side of the Champlain and Hudsoi] valleys, as 

 a result of which the newer seem to pass below the older and 

 more crystalline rocks, is well known. It is easy to conceive 

 that lateral pressure, from the contraction of the earth, acting 

 upon horizontal strati deposited against a barrier of older and 

 resisting rocks, may, according to circumstances, either cause 

 them, by the sliding of their edges, to be raised up and made to 

 dip away from the older rocks (a case frequently met with) — or 

 else, the edges remaining fixed, the compressed strata beyond will 

 be upraised in one or more folds (which may even be over-turned) 

 often with faulting, so that the proximate portions are made 

 to dip towards the resisting barrier. This condition, as was 

 well shown by H. D, Rogers, is seen in the Primal and Auroral 

 strata along the north-west base of the South Mountain in the 

 great Appalachian valley. We have here at Port Henry 

 apparently an example, on a small scale, of the same phenomenon 

 on the opposite side of the valley, and against the southeast base 

 of an ancient barrier of Laurentian gneiss. 



