416 • NEW YORK: STATE MIJSEtJM 



sets in the Precambric rocks, but, because they appear less 

 well marked, some hesitancy is felt in ascribing both to a single 

 time of joint formation, specially in view of the evidence for 

 the prior existence of at least an east-west set in the Precam- 

 bric rocks. It is inferred rather that the coincidence in direc- 

 tion is merely a coincidence. 



In the shaly rocks of the Cumberland head series, in the 

 vicinity of Lake Champlain, the stresses which accompanied the 

 folding of the district to the eaistward were suifficiently felt to 

 produce cleavage in the weak shales, though the more massive 

 limestones and sandstones beneath were not affected. These 

 shales are found cut by closely parallel cracks with hades of 

 from 30° to 60°. The beds lie nearly horizontally, and this 

 cleavage angle indicates rather a formation of fissility along 

 the shearing planesi than a true vertical cleavage jn the com- 

 pression plane. Sharply cut, vertical joints are also present, 

 often in three directions. While the writer has never observed 

 a like structure in any of the Champlain Utica which he has seen, 

 yet the Utica always shows more indications of compressive 

 disturbance, so far as folding is concerned, than any of the 

 remaining Paleozoic rocks of the region. The explanation is 

 undoubtedly to be found in the weak nature of the rocks as 

 compared with the* massive, resistant limestones and sand- 

 stones beneath, so that folding and shearing were produced in 

 them by forces insufficient to affect the others correspondingly. 



TOPOGRAPHY 



Introduction. 



The topography of any old land area lis a resultant of the 

 joint action 'of two great sets of processes. Arising from be- 

 neath sea level with the comparatively smooth surface which 

 it possesses because of the rather uniform deposit of sediments 

 on it, it becomes at once subject to the erosive processes which 

 hold sway on all land surfaces, in which atmospheric and 

 aqueous agencies act jointly, but in which running water plays 

 the major role. From time to time it falls under the influence 

 of forces such as that which originally brought it above the 

 sea level, forces originating in the earth's interior in waysi not 

 well understood. These vary its altitude with respect to that 



