CHAPTER III. 



. u. BKETOH Of TIIK I Of MICHIGAN, AND US CONNECTION 



Willi BURROUNDINS DISTRICTS. 



The rocks which constitute the solid crust of our earth may 

 be arranged into great groups according to the following plan: 



ti RATIFIED. 



1' esiliferous. 



tc, "i" nnfossiliferous. 



l\ -rRATIFIKD. 



\ lc u ic, S8 lava, trap, tVc. 



Pint lite, Byenite, &c. 



aking, the Fossiliferous strata are higher 

 than i A c, while the place of the Plutonic is generally be- 

 low ti. j aud the relative antiquity of these three classes 

 of rocks is represented by this order of superposition. The 

 volcanic rocks have burst up through the other rocks at various 

 cue is to somo extent true of the Plutonic — 

 lites appearing to have been formed since the 

 granitic substratum <>{' the Azoic rocks was formed. The Upper 

 aula furnishes us with abundant examples of all these 

 a of rocks. After devoting a lew words to the unstrati- 

 we shall pro speak of the stratified, as nearly 

 ssible, in chronological order, beginning with the oldest. 



I.— PLUTONIC GROIT. 

 A belt of granitic rocks comes down from tin 1 northwesl into 

 northern VViaconsin, ami em - a few miles orer she Mich- 



igan boundary line between Montreal river and Lac Vieui 

 D rt At the -urface tii ted by a bell of 



rocks from mass of granite, which ts probably a oontin- 



natioD of the fii :* the 



1 extendi gradually widening, until it 



occupies th i back from the I 



the way from the Enron rirei to Preeqne Ish-, at which two 



