POPULAR EXPLANATION. 21 



After the explanation of the northern origin of the drift 

 that has jnst been given, it need not excite any surprise to find 

 in it various kinds of materials that did not originate where 

 they are found. It is not unfrequently the case, however, that 

 certain unusual substances are found in it which excite more 

 than ordinary curiosity and interest. Such for example as 

 lumps of copper, fragments of lead ore, wood, lumps of coal, 

 and in rare instances also traces of gold. The occurrence of 

 these substances in the drift in no case indicates an exception 

 to the northern origin of much of the drift materials, for 

 we have evidence that the glacier currents were seldom if ever 

 directly south, but that they were variously deflected from 

 that direction. Thus it is proper to infer that the lumps of 

 copper might easily have come from the copper-region of 

 Lake Superior; the fragments of lead-ore from the Dubuque 

 lead region; the traces of gold from the northern part of Min- 

 nesota; the wood from forests which were growing when the 

 glacial epoch commenced, and those lumps of coal which are 

 found in the drift to the northward of the borders of the coal- 

 field, doubtless came from a thin bed of impure coal that is 

 known to exist in the Cretaceous strata of southwestern Min- 

 nesota. It is then almost needless to say, that the presence 

 in the drift of such isolated lumps of coal is no indication at 

 all of the existence of regular beds of that substance in the 

 same vicinity, any more than the lumps of copper indicate 

 valuable deposits of that metal, or than the granite boulders 

 indicate the existence of regular ledges of granite where they 

 are found in the drift. 



People throughout the State have very often asked the fol- 

 lowing questions, by letter and otherwise: What relative 

 position do beds of coal hold to limestone, sandstone, or 

 other strata? What is "coal blossom?" or, what is a sure 

 indication of the presence of coal beneath the surface? The 

 terms " coal blossom" and "oil blossom" are not used by 

 geologists, nor by any one else having correct scientific know- 

 ledge and a proper regard for the English language, but those 

 who do use such terms, appear to mean the presence of 



