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nently, which shows that in the gneiss, as in the conglomerate, 

 the mica, feldspar, etc., are not in layers, but strings. On 

 account of possessing this semi-fibrous structure, the dip of 

 the gneiss is not always easy to determine. Simultaneously 

 with the alteration of the conglomerate to a gneiss-like rock 

 the arenaceous and argillaceous beds are changed with less 

 difficulty to quartzite and mica slate ; though it is likely that 

 much of the true argillite must always remain essentially 

 unaltered, being, for chemical reasons, insusceptible of meta- 

 morphism. 



As already remarked, conglomerates exhibiting extensive 

 alteration are known to occur at many points throughout New 

 England; and the number of these localities will probably be 

 increased by more extended and careful observation. These 

 conglomerates are probably of several different ages ; and 

 yet the metamorphic process appears to have been substan- 

 tially the same in every case. As a rule, the altered conglom- 

 erate is closely associated, geognostically, with gneiss or mica 

 slate ; and in every such instance the product approximates to 

 one or the other, or both of these rocks. All observers agree 

 that these remarkable passages of sandstone and conglomerate 

 toward mica slate and gneiss are due to alteration and not to 

 derivation ; there can be no doubt on this point. And yet, as 

 previously stated, the gneiss-like products of the alteration of the 

 conglomerate are frequently difficult to distinguish from the 

 schistose gneisses forming a large part of this great gneissic 

 formation. Such identity in the effects seems to imply similarity 

 in the causes, some community of origin ; and I am somewhat 

 inclined to regard the small area of semi-crystalline rocks in 

 Bellingham as essentially a part of the gneiss and mica slate 

 formation, and to see in the more conglomerate portions an in- 

 dication of the condition of a large part of our schistose 

 gneisses at some time in the remote past, — a small sample 

 arrested in its development, and now available as a key to the 

 origin of thousands of square miles of crystalline rocks. 



To recapitulate briefly, we may say, concerning the genesis 



