MUSEUM OF COMPARATIVE ZOOLOGY. 



203 



greater or less extent — sometimes by a score of miles — of imbrokeu 

 strata. The same reasoning that wonld make the district sonth of 

 KtaaJo a continuous granite area, would apply as well to others known 

 to be underlaid by strata through which granite shows itself in detached 

 hills or ridu'cs. 



The case of Augusta, situated near, but not at, the southern border of 

 the region of slates and schists, is instructive in this connection. The 

 conclusion wliich even a geologist looking over that vicinity in haste might 

 feel to be the natural inference from obvious and abundant data, would 

 nevertheless be a wholly false one. An outline of the case only can here 

 be given. Augusta city is built on both sides of Kennebec River, upon 

 well-developed terraces which form the sides of a valley that has there 

 been excavated to the depth of 300 feet below the level of the adjacent 

 country. The width of the valley cast and west, from snnnnit to sum- 

 mit, is a little over one mile in a straight line, and midway runs the 

 river in a course somewhat west of south. The terraces and suftimits 

 on either side are composed of drift deposits, so thick that the deepest 

 wells nowhere reach solid rock ; and four sharp ravines, that on the 

 western side cut the terraces down to the level of the river at their 

 mouths, have bottoms and sides of drift, as has the river bed, except at 

 two points. The highest part of the western summit is a "granite" 

 ledge which rises in a knob some thirty feet above the rest of the sum- 

 mit and the general level of the country. Its top has an area of not 

 more than one or two acres, and falls off rapidly on the north, east, and 

 southeast beneath the enveloping drift. A mile south of this point, and 

 half a mile southwest from the State House, is a broad hill, about 400 

 feet in height above the river. On its soutliwest side, which lies in 

 ILillowell, are the quarries that furnish the well-known *'Halloweil 

 granite." The hill throughout is a solid mass of the same material. 

 In riding out of town two miles to the west, northwest, or northeast, one 

 comes upon several "granite" quarries in each direction. In view of 

 the foregoing facts, a visitor woxdd feel himself justified, if no further 

 examination were made, to pronounce "granite" to be the underlying 

 rock of the vicinity. But should he notice just across the railway track 

 from the station, at the foot of the second terrace, forty feet above the 

 i-iver and 200 feet from it, an exposure of rock now mostly hidden l)y 

 n, granite bank-wall, he woultl find it to consist of hardened, upturned 

 schist; and in the drought of summer he would see in the river i)ed, 

 for a few rods above and below the railway bridge, ledges of the same , 

 schist. 



L 

 h 



r 

 I 



T 



1 

 1. 



i^ 



