338 Lieut-Colonel Portlock on the Absence of any Traces 



logist is now familiarized with the fact that sea and land ex- 

 isted contemporaneously even at the period of the now meta- 

 morphic schists, and at each succeeding geological epoch, and 

 is accustomed to strip off, as it were, the accumulations of 

 more recent deposits, in order to study the condition of the 

 earth's surface at a period antecedent to them. Whilst, how- 

 ever, we thus rightly and wisely adhere to the system of reason- 

 ing from those facts which we are enabled to study and esti- 

 mate in all their bearings, we must not forget that there are 

 also facts which we can only partially study and imperfectly 

 estimate : for example, astronomy gives us strong reasons for 

 believing that it is more than probable that whilst some sidereal 

 and planetary systems may be coming into existence others are 

 passing away even at the present moment, and that an exact 

 balance in the universe has not been yet attained. It teaches 

 us, therefore, that we cannot always measure the possible ex- 

 tent of action of any given force by the effects it exhibits at any 

 one period, and that interfering or co-operating causes may 

 often tend to diminish or to augment its energy. I have been 

 led to make these remarks by the accidentally simultaneous 

 notice of the two subjects of this article, at the Geological Sec- 

 tion of the British Association at Swansea ; the first by the 

 Marquis of Northampton, in describing some recently fallen 

 aerolites, and the second by the Dean of Westminster, in again 

 bringing forward his discovery of the traces of ancient glaciers 

 in the Snowdonian chain of North Whales. It had been long 

 familiar to my mind that geological investigation had hitherto 

 discovered no traces either of the fall of aerolites or of glacial 

 action in the ancient strata of the earth's surface, and I there- 

 fore made a few observations on the papers read, with a view 

 to direct the general attention of geologists to the fact, or to 

 draw from them any statements of observations tending to in- 

 validate the conclusion, and to carry back to past systems 

 those remarkable phaenomena of the present. It appeared to 

 me that none of the eminent geologists present were prepared 

 to doubt the accuracy of my conclusion, so far as it depends 

 on facts hitherto observed ; but there seemed to be an impres- 

 sion that the number of falling aerolites is even now so small, 

 that the chances of meeting with them are few, and that such 

 chances must be still rarer in the examination of ancient strata. 

 This opinion I do not consider to be well-founded, as it must 

 be remembered that the study of these interesting bodies is com- 

 paratively recent, and that there is now every reason to believe 

 that the number falling is -very considerable, though from 

 many natural circumstances a large portion of them may fall 

 unobserved ; and so far from the chances of observation being 

 fewer in the examination of the ancient strata, I consider the 



