586 M. AU ROUSSEAU AND HENRY S. WASHINGTON 



SUMMARY 



The scattered contributions to the geology and petrology of 

 the alkalic igneous rocks of northern New Jersey are reviewed in 

 chronological order, and a general account of these rocks is given. 



The large mass of nepheHte syenite northwest of Beemerville 

 is described and is interpreted as a lenticular sill or a flat laccolith 

 of foyaite, intruded by a mass of nephelite porphyry (probably a 

 dyke) and by a small dyke of leucite tinguaite. 



New analyses of the nephelite syenite (foyaite) and of the 

 nepheHte porphyry are presented, and the afl&nities of these rocks 

 and of the leucite tinguaite are discussed. It is concluded that 

 these three rocks are textural and mineral variants, without chemical 

 differentiation, of the same magma. 



It is shown that the nepheHte porphyry is not a sussexite, as 

 formerly supposed, and the status of sussexite as a rock variety 

 is considered, with the conclusion that the name should be retained 

 in its original sense, but that the nepheHte porphyry of BeemerviUe 

 can no longer be regarded as the type of the variety. 



The presence of zirconium and the rare earths in the Beemerville 

 rocks has been demonstrated, and the wide distribution of these 

 elements in the region east of the Appalachians is briefly discussed. 



Washington, D.C. 

 April, 1922 



