COURSES OF THE EARTH'S MASONRY. 75 



proceeded a little farther with our talks. Secondly, since the 

 lowest rocks of which we can gain any knowledge are not 

 such non-sedimentary foundation, we are unable to affirm 

 that we have ever explored to the bottom of the sedimentary 

 rocks. There may have been underneath, originally, a vast 

 additional amount of strata. We will study the oldest strata 

 accessible to us, and observe how they lie in respect to the 

 later strata. 



If we travel over the surface of the country, we find it 

 generally overspread by loose materials which, in the northern 

 states are the so-called Drift. But here and there the bed- 

 rocks appear at the surface. That is, they outcrop. The na- 

 ture of the outcropping rocks is various. Sometimes they 

 are limestone, sometimes sandstone, sometimes shale, some- 

 times granite or some other sort of crystalline rocks. It seems 

 at first, as if every thing were in a state of confusion. But 

 let us be patient ; we shall discover order. We shall perceive 

 that one sort of stratum passes under another, and perhaps at 

 the distance of some miles, comes to the surface again. We 

 shall notice that a different stratum or formation passes under 

 this, and then perhaps comes to the surface again at some 

 point still more distant as if they were three wooden dishes 

 in a pile J., the largest; B, the next in size, and 0, the 

 smallest. B goes down under 0, and comes up beyond C. 

 A goes down under B, and comes up beyond B, on the op- 

 posite side. Many times numerous successive strata are nested 

 in each other precisely in this fashion. The lower peninsular 

 of Michigan is a good example. If you refer to the Table on 

 page 73 you will see that the Coal Measures are underlaid 

 by the Conglomerate Measures, the Carboniferous Limestone, 

 the Catskill Group, the Chemung Group, the Hamilton 

 Group, and the Corniferous Group. Each of these formations 

 underlies the peninsula in the form of a broad, shallow dish. 

 The Corniferous Group is at the bottom. Its margin comes 

 to the surface in southern Michigan. You see it in the lime- 

 stone at Monroe and throughout that region. Thence it 

 passes under the state and comes to the surface again at Old 



