202 REPORT OF THE 



course outcrop successively on the higher levels, several miles 

 back from the lake shore. These, like the more solid water- 

 bearing' strata, carry the water from the surface along imper- 

 vious floors jgun til it passes under the city, and finds its way 

 into the artesian borings. 



From what has been said of the occurrence of outlying 

 patches, or small detached basins of carboniferous rocks, and 

 the gently undulating character of the whole system, it will at 

 once be inferred that besides the great basin? just alluded to as 

 reservoirs of water, there must be numerous smaller local 

 basins. The indications seem to justify the conclusion that the 

 wells at Jackson are supplied from a local basin. It appears, 

 therefore, that a reliable opinion on the prospect of success at 

 any particular point involves not only a knowledge of the gen- 

 eral conformation of the rocks, but also an acquaintance with 

 the special geology of the region in question. 



In those portions of Calhoun, Jackson and Hillsdale counties 

 which are situated over the outcrops of the Napoleon and Mar- 

 shall sandstones, very many of the common wells terminate ia 

 these rocks, and from them derive their supply of water. 

 Nearly all the wells of the Lower Peninsula, however, derive 

 their supply from the sands of the Drift, The materials of the 

 upper portion of this formation have been, by geological agen- 

 cies, considerably assorted, so that beds of arenaceous mate- 

 rials alternate with beds of argillaceous materials, as in the 

 underlying rocks. There is, however, no general stratification 

 of these deposites Every bed of sand is comparatively local. 

 No general parallelism can be traced among them. The argil- 

 laceous layers of the drift may be compared to a pile of woodea 

 bowls thrown confusedly together — the interspaces being filled 

 with sand. At one point, a well will be found to be within the 

 rim of a given bowl, while at a very short distance from that, 

 an excavation would prove to be outside of the same basin and 

 would have to be carried perhaps to a much greater depth be- 

 fore reaching the bottom of the basin which underlies. On ttio 

 University grounds, wells are sunk 70 to 80 feet before reach* 



