202 THE GEOLOGICAL AGE OF CENTRAL AND WEST CORNWALL. 



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Here d2 is from near the Nare Point, part of the same 

 stone as that represented by analysis d in the Table I. The 

 diJfferent ratios of potash to soda appear to indicate an original 

 difference in the mineral composition, which perhaps facilitated 

 the weathering ; e is a moderately weathered rock from 

 Newquay. This latter contains also traces of sulphur and 

 nickel, /is the mean of two closely agreeing analj^ses of the 

 rock from Fiddler's Grreen ; (/ is the mean two similar analyses, 

 from Flushing ; h is from the Gannel ; / is from Roscreage at 

 the north western foot of the Beacon near Eoscreage House, 

 andy is from Beacon Hill, Falmouth, (the most decomposed of 

 all). Viewed broadly in the light of these analj^ses it appears 

 that weathering really or apparently decreases the combined 

 water, increases the silica and oxides of iron, decreases the 

 alkalies and alkaline earths. 



In aR these rocks there are also traces of phosphoric acid, 

 manganese, lithia, and fluorine. lu the rock from Trelissick 

 {a, b) the high proportion of alkalies is notable — also the fact 

 that the potash predominates over the soda. We have only 

 observed this in one other instance. This Trelissick rock also is 

 free from carbonic acid, which is different to what we have 

 observed in all other unweathered examples of the mica-trap. 

 The Lamb'Creek rock (c) contains much less combined water 

 than the others ; in the rock from near the Nare Point, the 

 alumina is exceptionally low, and the carbonates are exception- 

 ally high. 



