Geology of the Lake Superior Land District. 19 
There are undoubtedly, at this day, beneath the bed of the 
ocean, numerous “salses,” which, from time to time, pour forth 
streams of pulverulent materials, but whose operation is concealed 
from human sight. We know that for weeks in succession, there 
flowed streams of chocolate-colored mud from the crater of 
Graham’s island, before it finally sank below the surface. he 
contributions from this source, to the first formed stratified de- 
posits, had not been duly appreciated. This voleanic mud is 
nothing more than the comminuted particles of trappean rocks, 
reduced by friction ; and in the early history of our planet, when 
the fissures communicating with the interior were unfilled and 
volcanic energy was manifested more intensely than at this day, 
it would be reasonable to expect that igneous causes contributed 
as powerfully to the reduction of the preéxisting rocks, as the or- 
dinary abrading action of water. ‘The slates are composed essen- 
tially of the same ingredients as the trappean rocks with which’ 
they are associated, and the main difference between them may 
be, that the one was the product of salses, ejected in the form of 
mud, while the other was the product of volcanoes, ejected in 
molten streams. It has been supposed that the talcose nature of 
the slates associated with the igneous rocks was the result of 
Inetamorphism, but the supposition that they have resulted in 
some instances from the destruction of the latter, is quite as rea- 
sonable. 
About a mile from the lake shore, on the road leading to the 
Jackson Forge, a low range of trappean rocks, of a compact text- 
ure, and of a dark-green color, is intersected. Between the Jack- 
son and Marquette landings, by the lake shore, a similar belt is 
observed, which again appears near the junction of the roads, 
about four miles inland. 
Another belt intersects the coast a short distance above the 
Marquette landing, which does not differ essentially from those 
before described. The slates in the vicinity of these belts are 
compact, ofa greenish color, aud traversed by different systems of 
Joints, more distinct than the lines of bedding, cutting the mass 
into cuboidal. blocks. 
At Little Presqu’isle, another band of igneous rocks, of a highly 
crystalline character, projects into the lake. Distinct acicular 
crystals of hornblende are distributed in places through a paste of 
Connected, the latter forming beds of considerable thickness. 
Angular fragments of hornblende slate, chlorite slate; jasper and 
@ green magnesian mineral, are seen enclosed in the mass near the 
Water’s edge which may be regarded as a volcanic breccia, These 
fragments seldom exceed a few inches in diameter. 
Like most of the rocks of this region, its surface is smoothed 
and striated in a wonderful manner. Below the mouth of Dead 
