432 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



served elsewliere in Massacliuaetts, cannot be douLied. Litliologically at least 

 it may be said to be sui generis in Massachusetts geology. The great disturb- 

 ance which the Naugus Head series everywhere exhibits, and its thoroughly 

 crystalline appCcarance, stamp it as older than the Hurouian and Montalban for- 

 mations. . . . ; What, now, are the geognostical relations of the Naugus Head 

 series to these Iluronian terranes ? It underlies them. Everywhere, along 

 the boundaries of the Naugus Head areas, we find the various members of this 

 series penetrating and cutting through the Iluronian rocks. But the converse 

 of this is never observed. Nowhere, so far as my observations extend, does 

 the Naugus Head series appear to be cut by the adjoining Huronian rocks ; 

 nor by any member of the Huronian system ; nor, in fact, by any rocks not 

 easily referable, as already stated, to the stratified portions of this seri(;s itself. 

 In short, the Naugus Head series appears to be, as it were, at the bottom ; and, 

 while it has been extravas-ated extensively through superjacent formations, it is 

 penetrated by nothing foreign to itself The Naugus Head series is cer- 

 tainly distinct from, and .... probably underlies, the Huronian ; and, snice 

 it bears no likeness to the Laurentian system, we are brought to the conclusion, 

 that, if it is to be correlated with any series already described, that series is 

 the Norian. In short, the Naugus Head series does not resenjlde the Lauren- 

 tian, and is, stratigraphically, where we should expect to find the Norian. 

 .... The only rocks in Massachusetts tluxt have been observed passing beh»w 

 the Huronian system, or cutting throngli its lower jneud:)ers, are those compos- 

 ing the Naugus Head series ; and this, together with its crystalline character 

 and immense disturbance, convinces me that this series is the oldest in tlie 

 State. In the light of our present knowledge the conclusion cannot be 

 avoided, that the Naugus Head series is the real base of the geological column 

 of Massachusetts." 



An examination of this so-called Norian or Naugus Head region and 

 its rocks, by Dr. Wadsworth, has shown that tbc chief rock is of similar 

 character to the zircon syenite of Norway, and that it consists princi- 

 pally of orthoclase, with hornblende and some microclhie and plagio- 

 clase, together with rnicroscopic and macroscopic zircons. The feldspar 

 has the same inclusions as that of Norway. At Naugus Head a dark 

 micaceous schistose rock occurs. Througli this schist the syenite has 

 been erupted, forming long bands parallel with the foliation. These 

 bands vary from a fraction of an inch to many fcot in thickness This 

 structure strikingly resembles stratification, and has been tak^n as 

 such ; bat, if a careful examination is made, it will be seen that the 

 syenite follows the foliation only approximately, and that after running 

 some distance it suddenly shoots across the foliation into other ban<ls. 

 Fragments of the schist arc abundantly enclosed in the syenite, while 

 dikes of the latter can be seen cutting directly across the schist. 



