10 



PHYSICAL GEOGRAPHY. 



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Nova Scotia and Pennsylvania. His 

 ideal section represents the New 

 Hampshire rocks as granite at the 

 White Mountain centre, with gneiss 

 upon both sides, dipping on the east 

 towards Maine, and on the west 

 towards Vermont. The schistose 

 rocks adjacent to the gneiss in 

 Maine and Vermont are called " Cam- 

 brian." The Green Mountains of 

 Vermont are made out to be an 

 immense stratum of quartz rock, dip- 

 ping westerly. These Cambrian stra- 

 ta in their turn are flanked on their 

 outer sides by Silurian, and these in 

 their turn by Carboniferous rocks, in 

 the extremes of Nova Scotia and 

 Pennsylvania. 



Not to be misunderstood, I have 

 reproduced here Dr. Jackson's ideal 

 section. I shall attempt hereafter 

 to point out that in this idea there 

 is an important element of truth, 

 while many of the details are incor- 

 rect. It is true, for instance, that 

 in the White Mountain neighbor- 

 hood the older rocks make their 

 appearance. This view is derived 

 from the study of the formations in 

 the field, and is at variance with 

 the prevalent opinions of Amer- 

 ican geologists, as held in i868, 

 when our explorations commenced. 

 The quotation given in Chapter ii 

 shows that our first explorations 

 about Lisbon led to the conclusion 



