ON THE DETRITAL TIN-ORE OF CORNWALL. 195 
but here and there they are so closely grouped as to afford mutual 
support. Some of them rest on the vegetable mould, others touch 
the gravel and shingle ; usually, however, they reach—and a few 
intrude on—the tin-ground,* but in no instance have they passed, 
quite throughout it, to the granite beneath. 
Near Benin in Sancred the bed of a confluent with the 
little vale which extends from Tregonebris to the coast at Lamorna, 
presents the following section :— 
(1). Granitic sand and gravel, mixed with small cools and 
subangular masses of granite.......... - 6 to 12 feet; 
(2). Peat; in which nuts and branches Saucon tes of therglle are 
imbedded herevand: theres sctetacsiepeselccs oasciae ses PAs nena ts tutes 
(8). Granitic sand, gravel, and pebbles, sparingly eatemepemad 
with large boulders of (AeA poo060b0 006000000000 a few inches; 
this—except that it is generally unproductive—differs 
but little from— 
Zennor, seven. 
1 Near the summit of Carn Galver ..........e.ee+..- Discovered and 
sketched by Mr. 
¢ Joseph Blight. 
IL Wo Oi Tae Clinsyday Gooquec00cc0unoebo0e oe eececene» Described (BLIGHT, ~ 
Land’s-End, p. 
220. 
1 Near Tregarthen-cottage (The Hagle’s-nest) .... ..... Undescribed. 
1 53 ) 5 " » §.W. .... Undescribed. Dis- 
covered by Cap- 
tain Pooley, of 
Trelyon. 
Photographed oy 
3 Half a mile 8S. of Tregarthen- pouees and a furlong 3 
130 Git Aerinavore OiRoveallXOlN 55 G604600500000020000 ae Os SHEA 
To a casual observer the three small logan-rocks on Tregarthen-hill differ 
but little from the other groups of granite scattered over the moist, furze- 
clad, surface; but on inspection a flattish rock, of small extent, is found to 
support—at two or three feet above the general level,—two contiguous rocks, 
of like mineral character, and on one of the two rests a third, of the same 
kind. All may be easily moved; and whenever one of them is set in motion 
both the others move with it, though to a smaller extent; but by application 
of a different force to each it may take a peculiar movement of its own. 
’ In 1769 logan-rocks existed at Bosworlas in Saint Just and at Karn-lehau 
in Towednack, (Bortasz, Antiquities of Cornwall, Second edition, p. 180, Pl. 
xi, Mig. 3); but in 1842 the former had ceased to be moveable, (BULLER, 
Statistical Account of Saint Just, p. 87, and of the latter no intelligence is now 
to be obtained. 
* Hnormously large masses of quartz rest on the tin-ground at Merry- 
meeting. HEnwoop, Cornwall Geol: Trans: iv, p. 61. 
