STANNARD’S ROOK. 197 
idea of the structure of this district. The map and sections of Keweenaw 
Point are compiled from all available sources, including original observa- 
tions and original deductions from the work of others. In this connection 
should be studied, by any one desiring to understand the stratigraphy of 
Keweenaw Point more in detail, the correlation chart by Marvine, with his 
admirable explanations, given in Vol. I of the Geological Survey of Mich- 
igan.’ ‘The Eastern Sandstone, and the relations which subsist between the 
stratigraphy of Keweenaw Point and that of other parts of the extent of 
the formation are considered hereafter. 
Stannard’s Rock.—Twenty-nine miles 8. 51° E. from the eastern extrem- 
ity of Keweenaw Point, and 43 miles N. 10° E. from Marquette, there is 
an isolated reef rising abruptly from very deep water. Above water the 
rock is only a few feet square, but the entire reef is some 3,500 feet in 
length, as I learn from a large scale chart furnished by the United States 
Lake Survey. This length is divided into two portions by a gap some 600 
feet wide, in which the water is some 40 feet deep, the depth in the open 
lake, just outside the reef, exceeding 600 feet. The northern portion of the 
divided reef trends northwest, and has above the 20-foot contour a length 
of some 1,300 feet and width of 800 feet. The southern part of the reef 
trends slightly east of north, and is 1,700 feet long by 50 to 300 feet wide 
above the 20-foot contour. To judge from the soundings of the Lake 
Survey chart, this reef and another more deeply buried ridge to the west 
of it, might be the outcropping edges of layers trending north and north- 
west, and dipping eastward at rather a high angle. 
Foster and Whitney, quoting from Mather, speak of the rock of Stan- 
nard’s Rock as a sandstone,” but the specimen furnished me by the kindness 
of Mr. John Chassells, of Houghton, Mich., is a dark-brown felsite. In the 
thin section this felsite shows a base composed of a mixture of quartz, 
which in part appears to be secondary, a considerable proportion of pink- 
stained non-polarizing matter, and many nearly to quite opaque dark-brown, 
black, occasionally (in transmitted light) red ferrite particles, of wholly 
irregular shape. There are also included numerous larger brown and black 
porphyritic particles, with crystalline outlines, which now and then appear 
1Vol. I, Part II, Chapter IV. 2 Op. cit., p. 20. 
