no The American Geologist. Al ~ 
A considerable ingredienl of magnetite, in the form of minute grains, 
is present. A magnet drawn through a handful of the pulverized clay 
usually brings forth more or less of tin- mineral. Along the lake shore, 
where the clay i- washed away by wave action, the magnetite is left as 
a deposit of black sand, mingled with the quartz sand of the beach, 
whence it may be collected in large quantities. The lower part of the 
i- usually very highly laminate, and passes, by alternation- and 
gradation-, into the subjacent beach deposit. The main mass of the 
formation presents little indication of the line- of deposit, but upon close 
inspection, minute lamination may he observed. The relation of thi- 
to the imbedded rock is interesting. As the laminae approach the frag- 
ments, the greater portion curve downward and pas- beneath it. while 
a portion curve over it. It would appear from this fact that the frag- 
ment- were dropped upon the surface of a yielding clay mass, and cov- 
ered by subsequent deposit. Near the southern extremity of this form- 
ation, it has, along the lake shore, a thickness of from 15 to 20 feet. 
At Whitefish bay, above Milwaukee, it is from 20 to 30 feet thick, near 
Ulao, 40 feet, and in the vicinity of Port Washington it reaches its max- 
imum observed thickness of j? feet, although it doubtless somewhat 
exceed.- this at some point-. At many place- along the lake -bore, ow- 
ing to slides and washing, it appears to have a thickness considerably 
exceeding this. 
It has a wide surface distribution. .... Commencing near Mil- 
waukee, it widens to the north until the Kettle range is reacheo. by 
which its western boundary is deflected to the eastward until it passes 
that barrier and swings around upon the western side, and passing the 
water-bed. occupies the Green Bay valley. It ascends this valley to a 
few mile- south of Fond du Lac. and reaches up the Upper Fox river 
beyond Berlin, while in the Wolf river valley it extends beyond Sha- 
wano. West of the bay it appears in much less amplitude than to the 
southward. 
From what has already been said concerning this and the underlying 
formations, no doubt remains that it was a subaqueous deposit. Its ex- 
tent should, therefore, indicate approximately the amount of the en- 
croachmenl of the lake at the time of its formation, and the altitudes 
to which it ri-e- are significant of the amount of relative depression 
that attended its formation, and hence an especial interest attaches to 
its vertical distribution. At its southern extremity, it reaches an alti- 
tude of a little more than 100 feet above lake Michigan. Where its 
western limit crosses the north line of Ozaukee county it is about 200 
feet. A few miles east of this it rises upwards of 300 feet. At the 
northwest corner of section 36, town of Lynden. Sheboygan county, it 
is 315 feet. In the town of Rhine, of the same county, the limit is found 
at ^22 feet: at the middle of the north line of section 21. town of Mt- 
mee. Manitowi c county, at 248 feet, and on the opposite side of the 
Kettle range, at St. Nazian, at the same height. Xorth of this its limi- 
tation i- less well defined. There are some indications that it 
entirely over the Kettle range, in the central portion of Manitowoc 
