PORTAGE GROUP. 239 
three or four hundred feet of thickness exposed, which, together with what is exposed on the 
lake shore, makes the aggregate thickness little less than fourteen hundred feet. 
From the great breadth of surface occupied by this group, if the dip southward w r ere uniform, 
its thickness would be much greater than here estimated ; but it is evident, from numerous 
observations, that there are undulations which materially affect any calculations based upon 
the dip of the strata. By carefully examining the best natural sections, it appears that the 
average dip is about twenty-five feet in the mile; though in many localities, and indeed the 
greater number, the amount of dip is twice as great as this. In these cases, however, no 
account of the undulations is taken. 
Minerals of the Portage group. — The concretions contain crystallized carbonate of lime, 
and sometimes sulphate of baryta. Iron pyrites is freely disseminated through the rock ; and 
from its decomposition, the surface of the slaty laminae and the sides of joints are often stained 
with iron. It also gives origin to sulphate of lime or gypsum, which often coats the shaly 
laminae, or appears in the form of small crystals in the seams and joints of the same. Car¬ 
bonaceous matter is disseminated through the black shales, and sometimes appears in seams 
of half an inch thick. Some fragments of large vegetable forms appear, and thin laminae of 
coal usually accompany these. From the frequency of these small seams of coal, which are 
usually of no greater extent than the specimen procured, excavations and borings have been 
undertaken in search of larger beds. It is unnecessary to say that these always fail, as do 
all similar undertakings in rocks of this period. It is, however, impossible to prevent such 
useless expenditure of time and money, except by some source of information which can meet 
every one, and which shall find its way to all parts of the State. 
Springs. — The country underlaid by the rocks of this group is well watered by never- 
failing springs. It must be remarked, however, that the practice of indiscriminately clearing 
the woods from hills and valleys will in time operate injuriously on the surface, by drying up 
those sources which now supply the pure and healthful springs which water the surface, re¬ 
freshing both to man and beast. Except where the black slaty shale is thick, there is no 
difficulty in procuring water. In such instances the vertical joints appear to be more open, 
and to allow the percolation of water through the mass. There is here no remedy but to 
bore through the black to the green shales, which are less divided by joints, and usually 
impervious to water. In the present state of the country, however, there is little difficulty in 
procuring the desired supply, and that with little labor or expense. If the true origin of springs 
was known, and the means taken to protect them, there need never be wanting a sufficient 
supply of water on the surface. By the present practice, however, of cutting the wood from 
the higher grounds, many of the springs and smaller streams will eventually be dried up. 
Agricultural Characters of the Portage Group. 
In some parts of the country occupied by this group, we first notice a deficiency of calcareous 
matter in the soil. This change is indicated by a different growth of timber, and a correspond- 
