Correspondence. 425 
Minnesota, which next east from the Narrows of Red lake rises very 
prominently to a hight of 150 to 200 feet for a distance of about ten 
miles upon the peninsula dividing the northern and southern parts of 
the lake. Like nearly the entire western half or two-thirds of Minne- 
sota, this whole region is deeply drift-covered. No outcrops of the bed- 
rocks have been yet found on the large portion of the Red river basin 
lying in Minnesota; but the conspicuous escarpment of Cretaceous shales, 
overspread by drift, along the west border of the Red river valley, wells 
penetrating to Cretaceous beds along this great valley plain, and the 
topographic features of the land rising eastward from it with nearly 
the same rate of ascent as on the west, lead to the belief that the eastern 
like the western border of this wide valley is formed by an escarpment 
of Cretaceous shales beneath thedrift,and that an outlier of these shales 
enveloped by drift forms Beltrami island. It was long ago pointed 
out by Prof. N. H. Winchell that originally the Cretaceous strata ex- 
tended over all the western two-thirds of Minnesota, and on the south- 
east almost to the Mississippi river, since they still are known lo be 
largely continuous under the drift; and recent discoveries by Mr. H. V. 
Winchell of Cretaceous beds at several places along the elevated Mesabi 
iron range in northeastern Minnesota indicate indeed that the Creta- 
ceous marine submergence probably reached to the present site of lake 
Superior. Warren Upham. 
May 12th, 1893. 
Mesozoic Granite in Pi.umas Coitntv, California, and the Cala- 
veras FoKMATioN. In a review of Mr. Mills' paper on the "Rocks of 
the Sierra Nevada,'** the writer makes the statement "that there is 
thus no evidence extant that the granite of Plumas county is intruded 
into rocks later in age ihan the Carboniferous." 
In making the statement I had overlooked a paragraph in Mr. Diller's 
paper on the " Geology of the Taylorville Region," p. 301, where occurs 
the following: 
"Thedioritic rocks of the region are a portion of the great granitoid 
mass of the upper Sierra Nevada, and are evidently eruptive, with well 
defined contact phenomena in Triassic formations. Their eruption is 
certainly post-Triassic, and may have taken place immediately at its 
close, or after the deposition of the Jurassic." 
The "Calaveras formation " on p. 309 of the same number of the Gk- 
OLOGiST is defined as including " all of the Paleozoic sedimentary rocks 
of the Sierra Nevada." This definition may be correct as to the rocks 
of the Gold Belt proper on the western slope of the range where all the 
evidence gathered points to the Paleozoic rocks being Carboniferous in 
age, but it was not intended to include in the "Calaveras formation" 
the Grizzly Mountain Silurian beds described by Mr. Diller, nor the up- 
per Carboniferous strata of Genesee valley, called by Mr. Diller the 
Robinson beds. These do not appear to enter into the composition of 
the main mass of the range. 
*Am. Geologist, vol. XI, May, 1803, p. 312. 
