INTRODUCTION. . Vill 



Desmodium sessilifolium. Traciescaiuia Vivtjiuic a. 



Draba Caroliniana. Utricularla resupinata. 



Eleocharis murata. Zi/.ia cordata. 



GEOLOGY, TOPOGRAPHY. AKD SOU.. 



Geologists have demonstrated that the Lowei* Peninsula of 

 Michigan is made up of layer upon layer of diti'erent kinds of rocks 

 formed as sediment, or mud deposit, when Michigan was part of 

 the great ocean. 



These rocks lie horizontally one upon the other, with Gratiot 

 County as a center. They rest upon a foundation of Arcluiean 

 rocks, and in the central part of the State they aie many thousand 

 feet thick. The upper and less extensive rocks were formed during 

 the Coal Period. The sedimentary rocks represent, with the greatest 

 regularity of position, nearly all the known formations of this con- 

 tinent, from the Cambrian, which is near the base of the rock 

 series, to the latter part of the Carboniferous Period, whose rocks 

 are well up towards the top of the series. Grand Rapids i.« situat- 

 ed near the edge of the Subcarboniferous series. 



After an interval, when Michigan had become dry land and tliesi' 

 strata had been cut by river valleys, came the Glacial Period, or Ice 

 Age, when vast sheets of ice moved from the north slowlv south- 

 ward as far as the vicinity of the Ohio River, They bore a great 

 amount of debris — rock, gravel, sand, etc., from the largest boul- 

 ders to the finest clay, and covered the entire peninsula with a 

 thick deposit, called by geologists the glacial drift. In places the 

 deposit is a commingled mass of rock-fragments of all sizes imbed- 

 ded in the clay, while in others it consists largely of material 

 which has been assorted by water, i. e., sand and gravel. 



Of the glacial, or surface, geology, Dr. A. C. Lane says: "The 

 ice front formed three lobes, one of which, the Lake Michi- 

 gan lobe, came up Lake Michigan; another, the Saginaw Bay 

 lobe, came up Saginaw Bay; and a third, the Huron-Erie lobe, 

 extended south-west from lakes Huron and Erie, covering the south- 

 eastern part of the State. Between each two lobes there was an angle 



