L2 
If any of the secondary formations were deposited in this county they 
have all been swept away so completely that their very existence is more 
than doubtful. Allusion was made to the formation of fissures at different 
dates, some of which are filled with El van (Trap) and others with the ores 
of tin, copper, zinc and lead. Some of these traverse the fossiliferous as 
well as the igneous rocks. The subject of the paper, was a description of 
some of the alluvial formations of the county in order to point out their 
bearing on recent Geological Questions. For this purpose a section given 
by Mr. J. W. Colenso in the Transactions of the Royal Geological Society 
of Cornwall, was chosen as typical of many others occurring in various 
parts of the county. It was exposed at the Happy Union Stream Tin 
Works at Pentuan, near St. Austell. 
At the bottom lying on the rock is found what is termed the " tin 
ground" and for the sake of reaching which the excavations are made. 
This consists of the oxide of tin or tinstone in the form of sand, pebbles 
and boulders and is sometimes as much as 10 feet thick. The mode of its 
formation has occasioned much controversy on account of its comparative 
freedom from other ingredients. The various reasons brought forward in 
support of the different views on this point would be interesting but too 
lengthy for introduction here. It must suffice to say that the tin ground 
is most likely the washings of the county during a long series of years. 
The absence of other material may be rationally accounted for by the great 
weight of tinstone (Sp. Gr. 7.0), nearly that of Metallic Iron, and its hard- 
ness, almost rivalling that of quartz. The former quality would bring it to 
rest in the bed of the stream where the current was yet strong enough to 
sweep away all ordinary pebbles, few of which exceed 3.0 Sp. Gr. and the 
latter would enable it the better to resist the wear and tear to which it 
was exposed while rolled along by the water. 
On the top of the tin ground with their rootlets among the tin stones 
are found the stumps of oak trees with trunks of the same in such positions 
that they must have grown and fallen where they now lie. Twelve inches 
of dark silt follow and on the top of this occurs a layer of leaves, hazel 
nuts, sticks and moss of equal thickness. In the next bed occur the same 
relics with the bones and horns of deer and oxen. A piece of oak 
apparently shaped by the hand of man has also been found here. It was six 
feet long by two inches wide and half an inch thick. Twenty feet of sea sand 
follow, omitting some thin layers, with the same organic remains and the 
addition of some human skulls and the bones of a whale. The top of this 
bed is just on a level with the present low water mark upon the neighbour- 
