PURGATORIES. 217 



The rock here is the peculiar gneiss of the Green Mountains, dipping 35 E. The most important infer- 

 ence from the case is that a river once and for a long time poured over this spot, which in height is nearly 

 equal to the average elevation of the Green Mountains. 



4. In Wallingford, 150 feet above Otter Creek, is another case of pot-holes. 



5. Another example is in West Hartford, on the Central Railroad. The spot is 60 feet above White 

 River, and the pot-hole 17 feet deep. From this hole was extracted the beautiful sphere of granite, 2 feet 

 4 inches in diameter, which the visitor will find lying in front of the College buildings in Burlington of 

 which we have never seen the equal. Two of them were found ; but one was buried in the railroad. 



6. A more important case occurs in Plymouth, not far to the north of Tyson's Furnace. A large pond 

 is here planted amid the hills, as much as 1100 feet above 



the ocean. On its east side a small stream enters, along 

 which, for one or two miles, some of the most successful 

 gold diggings in Vermont have been opened. Just east of 

 the pond rises a sharp ridge, whose crest slopes for the most 

 part rapidly to the south, and terminates at the stream, 

 as shown on Fig. 106. On the opposite side rises a cor- 

 responding hill, S. At A, about 250 feet above the lake, is a 

 small but distinct pot-hole ; and all along the crest of the 

 hill, which slopes rapidly both east and west for 40 or 50 

 rods, each way from the pot hole, are the most distinct marks 

 of water having poured over the ridge from east to west. 



The tortuous channels worn out of the rock are not exactly pot-holes ; but they approach that form of 

 erosion, and, to an eye familiar with river action, are scarcely less indicative of the former presence of a 

 river. Still further north rises a lofty hill, N, which probably protected this ridge in part from the full force 

 of the drift agency, and therefore it retains so much evidence of fluviatile action. One perceives at once, 

 that the stream which now runs at the foot of the hill half a mile south once poured over this crest, to the 

 height at least of over 300 feet, and that its bed gradually moved southerly as it was worn deeper. The 

 present outline of the surface probably gives us only an imperfect idea of the whole amount of erosion, 

 since we cannot tell how much has been worn from the crest of the hill. 



PURGATORIES. 



There is another class of phenomena indicative of erosions, to which we have given some attention, but 

 to which we hardly know what name to give. In Massachusetts and Rhode Island, however, the gorges to 

 which we refer have received the quaint name of Purgatories. Near Newport in the latter State, where 

 numerous transverse joints cut across the conglomerate, the action of the waves of the sea upon the matter 

 between two joints sometimes wear it away, so that deep and long fissures are produced with perpendicular 

 walls. These are called Purgatories. Sometimes these gulfs extend entirely through the crest of a hill, as 

 at Button in Mass., and still are called Purgatories, though far away from the present ocean. It is this 

 description of these gorges which we find in Vermont. They generally occur at the summit level of differ- 

 ent streams ; in other words, where two streams belonging to different systems of rivers take their rise. Yet 

 the idea that these small streams, usually only brooks, produced the gorges, is absurd. They can be ex- 

 plained only by earlier and more powerful agencies. But we will first refer to a few examples. 



1. The Dixville Notch in New Hampshire, as it has been described by D. C. T. Jackson^ seems to us 

 (for we have none of us seen it) to be a typical example. We have there a cut from 600 to 800 feet deep 

 in nearly perpendicular strata of mica shcist, through which a road runs from S.W. to N.E., and two streams 

 take their rise, one running westerly to the Connecticut and the other easterly to the Androscoggin. In 

 some way or other, then, we may be certain that a gulf 800 feet deep has been cut through this dividing 

 ridge. Whether we admit or not with Prof. 0. P. Hubbard, in his valuable paper on erosions in New 

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