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134 REPUTED GORGE OF THE LYD. 
with asledge hammer in order to remove them. A very 
similar illustration of the same kind of peculiar 
force which the sea thus exerts may be derived 
from the most diminutive sea shells situated in 
“shell sand.” In these we continually notice 
grains of matter blocking up their mouths much 
to the obscurity of their characters about that part, 
and on application of a penknife or pin to the 
intruding body it is found to be so impacted as to 
resist the greatest exertions at dislodgement short 
of fracture of their peristomes. 
In a valley not far from my residence, among the 
pebbles which had accumulated there in the course 
of time when the river which traverses it was of 
greater size, were found some few years ago, “ tin 
pebbles” or small rounded blocks of tin ore tolerably 
pure, and it is further reported that the men occu- 
pied in the discovery of these, occasionally detected 
bits of gold. The remains of ancient stream-works 
occur at several spots along the course of the Yealm, 
two of them near the village of Yealmpton. 
— 
Those geologists who are proselytes to the new 
doctrine of Lyell, will doubtlessly look for illustra- 
tions in our district of the supposed power of rivers 
to cut extensive gorges in rocks, and will perhaps 
point to the passage of the river Lyd at Lydford 
Bridge as a beautiful instance of the force of river 
currents. I feel persuaded that our county can 
produce but very limited proofs of the cutting power 
of streams even where the land would apparently 
suffer it without great opposition, and certainly, 
we can shew no instances indicative of the ability 
of rivers to effect emportant geological alterations— 
in short none but secondary geological results. 
With regard to the passage of the Lyd, I have no 
question but that the force of the torrent more 
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