250 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



We had hoped to have found similar in the large Pothole, whether 

 such will be, remains to be seen. It might possibly be, that they 

 have rolled out thiongh the passage at the bottom of the hole and 

 must be sought elsewhere. 



No. 3 being small was emptied and some of the finest specimens of 

 small rounded stones wei-e got from it. Nos. 2, 4, G, 7, have not 

 been examined, and it is probable that an examination of them will 

 meet with even more gratifying results than those emjjtied. Having 

 had the pleasure of seeing the Potholes at Lucerne in Switzerland, it 

 does seem to me that at Rockwood there is as interesting a series. 

 Along the river near the quai-ries 18 more or less defined holes 

 appear, and in this locality under consideration 12 in all are found, 

 and of these the seven more particularly describeil are exceedingly 

 unique in form, position and structure, and were they near a large 

 city would be a source of gieat attraction to visitors interested in the 

 works of nature. 



3. — Formation of the Caves and Potholes. 



In all districts, where limestone exists, it is not uncommon to find 

 caves, especially if water is near. Watei" containing carbonic acid 

 (a gas generated in the decomposition of vegetable material and 

 largely present in the atmosphere, from them the respiration of 

 animals ; for the air expelled from their lungs is charged with it) has 

 a powerful disintegrating eflect upon the carl)onates of lime and 

 magnesia, forming from them bi-carbonates, which are soluble in water 

 and as such are carried away ; consequently it is only a matter of 

 time before limestone (a carbonate of lime) when acted upon by water 

 containing this gas is completely dis,solved. A mere dripping in a 

 crevice will in time effect quite a change and form consideiable of a 

 cavity. If the quantity of water is considerable, the change is 

 accomplished in a shorter period. Very forcible examples of this 

 disintegrating effect of water on limestone were observed by me in 

 Derbyshire this summer. There are ravines there which are sujjposed 

 to have been formed out of the solid rock in ages long receded into 

 the past. 



These ravines were once overcapped by limestone, the cave or 

 passage itself dissolved and carried away by water, finally the top fell 

 in and the debris carried seaward, until now all that marks the great 



