GIBB — ON CANADIAN CAVERNS. 165 
perforated rocks. Altliough frequently seen by mariners and others, 
the only account published of them is in a paper by Captain (now 
Rear- Admiral) Bayfield, in the fifth volume of the Transactions of 
the Geological Society, second series, wherein a plate is given of a 
number of natural columns on the east coast of Niapisca Island. 
These curious columns are met with in most of the islands far 
above the reach of the highest tides, running along the ancient 
raised beaches. A picturesque group is found on the west side of 
Large Island, a mile to the northward of its south-west point. Here 
hundreds of flower-pot and arched rocks stand up out of the rising 
tide to heights varying from ten to fifteen feet on the flat limestone, 
with breadths from a few feet to thirty or forty, widening at the top. 
Many again are above high water mark ; and many straggling 
flower-pots are seen high up in the island, and with the succession 
of raised terraces strikingly illustrate the relative levels of the sea 
and land, when from fifty to sixty feet different to what they are at 
present.* A remarkable flower-pot rock is to be seen on the south- 
v^est point of the Outer Birch Island. 
According to Admiral Bayfield, most of them vary in height from 
fifteen to thirty feet ; some even exceed forty feet above the plateau 
of rock on which they stand. They are frequently arranged in lines 
upon terraces of limestone, precisely similar to those which are at 
present forming out of chffs that are washed by the waves. This is 
especially the case at the eastern end of Niapisca Island, where the 
largest and most remarkable group of these rocks is to be seen. 
It seems to me that there cannot be any doubt as to the manner in 
which these cmious natui'al objects have been formed, namely, from 
the effect of the waves at different levels, as we see the same process 
going on at the present day. Great or small holes are broken by 
the sea into the limestone cliffs ; these become larger and larger, 
spreading in various directions, when the roof of the caverns gives 
way, and leaves one or several pillars with a small base to support a 
partially arched top. The angular irregularities of the upper part 
of the pillar become worn away by the action of the sea and of the 
elements, as the land slowly rises, and we have what certainly 
resemble flower-pots, towers, and incomplete arches situated high up 
above the influence of the tides, and formed as it were of horizontal 
layers of limestone piled one above the other. 
A section of Large Island was found by Mr. Richardson of the 
Canadian Geological Survey, to be composed of limestones of the 
Chazy, Bird's-eye, and Black-river formations, exceedingly favourable 
to the wear of the sea into arches and perforations. Most of the 
other islands are formed in the same strata, the most northerly, 
however — Harbour Island, consisting of the calciferous sand rock, 
which lies immediately above the Potsdam sandstone ; whilst the 
maiu land is composed of gneiss belonging to the Lam-entian system. 
* Gcol. Siu-vej of Canada. Eepoft for 1856. 
