66 Captain Vetch on Icebergs* 



the colours of the supernumerary arches were ffreen and (as 

 appeared to my eyes) purple or violet. This splendid iris 

 (comprising primary, secondary, and supernumerary arches) 

 was seen at Bridlington Quay, August 12. 1826, at 5 p. m., 

 during a heavy partial shower of rain. The whole phenomena 

 conveyed the impression of a magnificent canopy of vertical 

 arches, or ribs of arches, diminishing in distinctness as if the 

 observer were looking into an immense structure, spanning 

 the heavens, of one grand arch, illuminated with ethereal light, 

 and enriched with the brilliancy of the precious gems. 

 Vicarage, Bradford, Yorkshire, May 19. 1841, 



Icebergs, and Changes of Geological Opinions. ' Communicated 

 in a Letter from Captain Vetch, F.G.S., &c., of the Royal 

 Engineers. 



Dear Sir — Since I had the benefit of receiving my first 

 lessons in mineralogy and geology, at your lectures in the Col- 

 lege of Edinburgh, many changes of doctrine have taken place; 

 and it is to be trusted that we are gradually approaching the 

 true theory, though the oscillatory movement of our progress 

 may occasionally place us for a while at a greater distance 

 from the object of our search. 



In the present day, the agency of icebergs is the fashion ; 

 and geologists are now much puzzled to find a sufiiciency of 

 cold and ice, in bygone days, to account for all the effects now 

 presumed to have been achieved by these agents. 



Som.e of our younger geological brethren may, however, 

 recollect the not very distant day when heat could not be found 

 enough, in past periods, to account for the great quantities of 

 presumed tropical plants and animals deposited in our now 

 cold regions ; and it is rather unfortunate that such great 

 demands have been made upon such opposite causes to afford 

 explanation of the phenomena of geology, since we place our 

 globe in the condition of having hot and cold fits, like a patient 

 under the visitation of an intermitting fever ; for I presume 

 the theory of a gradually cooling condition of the earth is 

 almoftt abandoned. 



