Smyth — Crystalline Kocks of St. Lawrence County. 



487 



suggests that they may be part* of one great series. This idea is strengthened 

 by the fact that on the borders of the gneissic areas, as the limestone is 

 approached, the gneiss is often finely laminated and quite similar to narrow 

 bands of gneiss which seem to be interbedded with the limestone. But these 

 laminated gneisses between the massive gneiss and limestone have been found 

 to be the exception, not the rule, as was formerly thought, and hence, are of 

 little importance in this connection. As to the parallelism of the foliation 

 of the gneiss with the strike of the limestone, it is a necessary result if the 

 foliation is a secondary structure resulting from the same pressure that folded 

 the limestone. 



The alternation of broad belts of limestone and of gneiss, in the north- 

 western portion of the region, is suggestive of a sedimentary series, in spite of 

 some peculiarities of distribution, difficult to explain ; but the scattered 

 patches of limestone occurring in wide areas of gneiss to the south and east, 

 are difficult to harmonize with this view. It has been thought probable that 

 the limestone was confined to the region of the extended belts, and that the 

 associated gneiss might be distinct from that of the southern and eastern parts 

 of the county. But, as shown above, the limestone has no such limitation, 

 and there is nothing to distinguish the gneisses of the northern townships 

 from those of the southern. They must be considered together, at least for 

 the present, as one great formation, with the limitations and conditions cited 

 below. It seems clear that if the gneisses of the northern towns belong to the 

 limestone series, those of the southern towns do as well. On the other hand, 

 if the latter do not, neither do the former. The reasons, so far as the relations 

 of the two are concerned, for regarding the gneisses as part of the limestone 

 series having been stated, it must be admitted that they are extremely inade- 

 quate. On the other hand, the gneisses themselves, with the exception of 

 limited areas, lack every characteristic of a sedimentary series. Thus, both 

 lilies of evidence fail almost completely to establish the sedimentary origin of 

 the gneisses. Nevertheless, the mere absence of proof that they are 

 sedimentary cannot be taken as proving that they have not this origin. For 

 it is entirely possible that the absence of proof results from extreme meta 

 morphisin, and the evidence sought for might be found at any time, provided 

 that some other origin can not be established. This latter condition leads to 

 the consideration of the second hypothesis named above: that of derivation of 

 the g misses from igneous rocks. 



Taking up first, as before, the internal evidence bearing upon the 

 question, there are certain characteristics of the gneisses that are of import- 



