TOPOGRAPHY. Xlll 



north-west, on the Cornwall side of the Tamar, between New Bridge and 

 the Weir Head, is another patch of this rock. Altogether granite occu- 

 pies rather less than one-sixth of the area. The granite of Dartmoor is, 

 as a whole, a coarse-grained mixture of quartz, felspar, and mica ; the 

 latter sometimes white, at others black, the two micas occasionally occur- 

 ring in the same mass. It is commonly porphyritic, from the presence of 

 large crystals of felspar, and here and there schorlaceous ; but the latter 

 character is chiefly confined to the outsknts, where the granite adjoins 

 the slates, as on Crownhill Down.* The gxanite on the west of the Tamar 

 is in composition very similar to that of Dartmoor. A band of Devonian 

 rocks altered through the intrusion of the granite comes in between it 

 and the rocks of the Devonian series. Around the margin of Dartmoor 

 the granite has thrown out veins, both large and small, into the adjacent 

 rocks.t 



Drainage. — The whole of the area has a southern dramage. The 

 number of its rivers constitutes one of its most noticeable natural features, 

 and makes it an easy matter to divide the country into botanical districts 

 founded on the natural drainage, though, from its comparatively small size, 

 it is not generally the entire basin of any river that can be dealt with. 



Proceeding from west to east the first river is the little Seaton, which, 

 rising between Caradon Hill and St. Cleer, after a course of about twelve 

 or thirteen miles falls into the English Channel at Whitsand Bay. It 

 di-ams a narrow tract lying partly within the parishes of St. Cleer, 

 Menheniot, and St. Germans, but only a portion of its basin is within 

 our area. 



The Notter rises at Beacon Hill, about two miles south-west of Altar- 

 nun, and after a course of twenty-seven miles % falls into the Tamar a 

 little below Saltash. For the greater part of its length, on to Notter 

 Bridge, it takes a south-east direction, receiving many small streams ; 

 those on its right bringing the drainage of the eastern side of the hills 

 about Caradon and to the north of the Cheesewring, and also of the 

 country lying east of the hills ranging from Caradon to St. Ive village. 

 The high road from St. Ive to Liskeard crosses the river just at the spot 

 where it comes within our boundary line. Between this and Notter 

 Bridge the drainage of the eastern portions of the parishes of Quethiock 

 and Landrake passes into it by several small brooks. A little below 

 Notter, close to which it is tidal, it bends shghtly towards the south-west, 

 continuing in this direction for about two miles, until it is met by the 

 Tidy, a small river from the north-west, bringing down most of the 

 drainage of the parishes of St. Ive, Quethiock, and St. Germans. A little 

 above its union with the Notter it passes under the old town of St. 



* De la Beche, Eep. pp. 157, 58, + Dr. Holl. 



X The lengths of the river courses are from De la Beche's Rep. Geo. Corn., Dev., and 

 W. Somerset. 



