GEOLOGICAL RELATIONS. I I 



known with precision ; but it is likely that future investigations will add 

 to their present representation upon the map, at the expense of the Lau- 

 rentian. 



Labrador System. All the known Labrador areas in eastern America 

 appear on this map. Five of them lie north of the River St. Lawrence. 

 One of the largest is situated a few miles north-west of Montreal, much 

 of it evidently concealed by the Lower Silurian groups. Next is a small 

 area bordering the St. Lawrence, on the Montmorency river, above the 

 falls. Its northern extremity is not over fifteen miles from the Murray 

 Bay area. A fourth is on the Saguenay river, below and east of Lake St. 

 John. The fifth is on the Moisie river, well towards Labrador. Still 

 another mass of labradorites has been recently reported in the south-west 

 part of Newfoundland. The Adirondack area is given as carefully as pos- 

 sible from Emmons's descriptions of his hypersthene rock. All these 

 terranes are accepted as types of the Labrador system outside of New 

 England. 



After the discovery of the physical structure of the granites and lab- 

 radorites of Pemigewasset, it occurred to me that several granitic districts 

 in Vermont might perhaps be included with it, and they are so delineated 

 on the map. They are in the northern part of Essex county, about Wil- 

 loughby lake, Craftsbury, and the high lands east of Montpelier. It may 

 be that Megantic mountain, Canada, belongs to the same system. There 

 are good reasons for believing that granitic rocks of perhaps Silurian age 

 have penetrated the earlier Labrador outflows in Vermont. Besides the 

 Pemigewasset and Starr King mountain areas, I have marked in the same 

 way the eruptive rocks of Red hill in Sandwich, Ossipee mountains east 

 of Winnipiseogee lake, and Gunstock. In Maine, the granite of Biddeford 

 closely resembles the Conway division of New Hampshire, while that of 

 Kennebunk is related to it. The Sanford area carries felsite ; while the 

 York division is like the sienite of Exeter, Dover, N. H., Gloucester, and 

 Quincy in Massachusetts. 



Htironian. The rocks referred to the Huronian cover immense areas. 

 A very important one, and the most characteristic of all, is that referred 

 to the Quebec group by Sir W. E. Logan. Beginning at Granville, Mass., 

 it passes into Vermont and Canada east of the Green Mountains, con- 

 necting not far from the province line with the wider belt starting at 



