FLOW OF STREAMS IN CORNWALL. 



303 



as 



of 41 "97 Ins. At Newquay 36*89 Ins. is the annual fall, and at 

 Trevose Head, the lowest rainfall in Cornwall appears to take 

 place of 24-56 Ins., which seems a little below what might be 

 expected at that point. Further up the coast, the yearly fall lies 

 between about 35 and 38 Ins., and on the country inland around 

 Wadebridge, from 37 to 41 Ins. 



The rainfall in the various districts may be grouped 

 follows : — 



Eainfall. 



The Scilly Islands 31 inches. 



„ Land's End District 30 to 42 



,, Lizard District 35 



Helston and Neighbovirhood . . . . 38 to 42 



Camborne ditto . . . . 42 to 51 



Truro and YaUey of the Fal . . . . 42 to 



St. Austell and Neighbourhood . . 48 to 



Bodmin Moors 50 to 



East Cornwall 40 to 



North Coast 



30 to 



45 

 50 

 65 

 52 

 38 



Part II. — The Flow of Streams. 



The proportion of rainfall which flows off the surface by 

 brooks and rivers, varies with the nature of the ground on which 

 it falls ; on steep moorland ground with primary rocks, very 

 little loss is sustained by absorption, the rainfall almost in its 

 entirety flowing off the district in the form of streams : whilst in 

 a chalk country the absorption reaches its maximum, and the 

 streams their minimum flow, and the contrast is a marked one 

 between the swift clear brooklet of the former, and the rounded 

 bowl shaped hollow without the trace of a stream, in the latter 

 formation. 



The gaugings given in the Table No. 5 were mainly taken in 

 the years 1865-6, at Truthan on the Eiver Allen, 4 miles to the 

 north of Truro. 



The basin lies on the southern slope of " The Backbone of 

 Cornwall," and is of an area of 1-76 square miles; the gauge 

 itself was situated at a height of 185 feet above Ordnance Datum 

 (or Mean Tide Level), and the hills around attain in some places 

 the height of 470 feet above the same Datum. 



