Notices from the Minute Books of the Geological Society. 565 



opinion that the physical outline of the country indicates considerable changes inci- 

 dent to the emergence of the land. The deep transverse valley which intersects 

 the mountain called Le Roule, a little to the east of Cherbourg, is stated to present 

 some interesting phaenomena. The eastern escarpment, from 300 to 320 feet in 

 perpendicular height, slopes gently to the south as far as the commencement of the 

 slate, where the descent becomes extremely rapid into the valley of theDivett. The 

 western side of the ravine presents similar features, but in a reversed position ; the 

 escarpment of quartz rock, crowned by the Telegraph, being to the south, and the 

 slope to the north, with a very gentle inclination till it reaches the sea-level. 

 These opposite interchanges of slope and escarpment are occasioned, Mr. Clarke 

 says, by the direction and prolongation of the beds of slate, the line of coast not 

 exactly corresponding with the junction of the schist and quartz rock. The south- 

 ern junction of the two formations is about half-way up the ravine, near a chapel ; 

 and in the quarries along a road leading eastward, the phsenomena exhibited at the 

 contact of the deposits are well- exhibited. Throughout the district the range of 

 the slate is marked by the fertihty of the soil and the occurrence of woods, but 

 that of the quartz-rock by a prevaiUng barrenness. 



Fragments of the latter formation are either scattered over the surface, associated 

 with clay, or compose mounds free from extraneous matter ; and they preserve the 

 characteristic form of the parent rock, the angles, measured " by a goniometer," 

 affording three constant quantities, namely 108°, 64°, and 83° (fig. 1.) ; and the 

 last angle measures also that formed by the production of two sides, which in the 

 actual specimens are cut off by the intersection of a third plane. Fragments of green 

 schist detached by the hammer at the natural joints, gave also the same angles, or 108°, 

 64°, and 83° (fig. 2.) ; so that there is direct evidence, Mr. Clarke observes, of the 



Fig. 1. 



Fig. 2. 



Fragment of quartz-rock. 



Fragment of green schist. 



VOL. VI. SECOND SERIES. 



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