_6th_. I received a specimen of slaty graywacke from Lake Superior. The
structure is tabular, and very well characterized. If there be no
mistake respecting the locality, it is therefore certain that this rock
is included among the Lake Superior group.[29] It was not noticed in the
expedition of 1820. I also received a specimen of iron sand from _Point
aux Pins_.
[Footnote 29: I found graywacke _in situ_ at Iron River, in Lake
Superior, in 1826, and subsequently at Presque Isle River, where it is
slaty, and fine even grained, and apparently suitable for some
economical uses.]
The thermometer has stood at 25 deg. below zero a few days during the
season. It was noticed at 10 deg. below, this morning. Notwithstanding the
decidedly wintry character of the day, I received a visit from Mr.
Siveright, a Canadian gentleman, who came across the expanse of ice on
snow shoes. I loaned him Silliman's "Travels in England and Scotland,"
feeling a natural desire to set off our countrymen, as authors and
travelers, to the best advantage.
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