552 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



so-called " Ouachita Uplift," consisting of slates, sandstones, and 

 novaculites of Lower Silurian age, and bordering these lie Lower 

 Carboniferous rocks resting conformably upon the Silurian. The 

 sedimentary rocks are but slightly disturbed, and whatever fold- 

 ing or fracturing has occurred, took place before the intru- 

 sions. For various reasons, the chief of which is that closely 

 related rocks occur in adjoining districts intruding Cretaceous 

 sediments, the age of the Arkansas alkaline rocks is considered 

 by Williams to be Eocene. In this region no earth-movements 

 involving great compression have transpired since the commence- 

 ment of the Silurian period. 



In New Jersey monchiquite dykes and nepheline syenite dykes 

 occur intruding the Hudson River and Oneida stages of the Lower 

 Palaeozoic. No later sediments occur in the region, so that it is 

 impossible to fix the age of the intrusions. Similar dykes have 

 been met with in the States of New York, Maine, Massachusetts 

 and adjoining States. 



Numerous dykes of bostonite, camptonite, fourchite, diabase, 

 and monchiquite occur in the Lake Champlain district, and have 

 been ably described by Kemp and Marsters.* These dykes 

 intrude Palaeozoic sedimentary rocks, the latest of which are the 

 Utica slates. Their age is therefore unknown. 



Post-Silurian elseolite syenites from Montreal have been 

 described by A. Lacroix,f and are also referred to by T. S. Hunt. J 

 They include trachytes and phonolites, and are associated with 

 dolerites and diorites. Harrington and Adams mention analcite- 

 bearing rocks and teschenites from the same district. Nepheline 

 syenite has been described from Red Hill, New Hampshire, by 

 W. S. Bayley,§ and by Bayley and Eakins from Litchfield, 

 Maine.|| Similar rocks have been described by F. D. Adams 

 from Dungannon, Hastings Co., Ontario, U forming a large mass 



* " The Trap Dykes of the Champlain District," Bull. 107, U.S. Geol. Surv. 



t Comptes Kendus, 1890. 



J Geological Survey of Canada, 1863. 



§ Bull. Geol. Soc. of Amer. Vol.iii. 1892, p.250. 



|| Bull. Geol. Soc. Amer. Vol.iii. 1892. p. 232. 



H Amer. Journ. Sci. xlviii. p. 10, 1894. 



