128 REPORT OF THE 



remarkable feature seen here, however, is the occurrence of 

 two parallel grooves crossing the first set and bearing N. 60° 

 E. These grooves are 4 ft. 6 J inches apart, 1£ inches deep, 9 

 inches wide, and 25 feet long, issuing from under the cover of 

 diluvial materials, and terminating at the point to which tho 

 waves have broken away the rock. The first impression which 

 irresistibly forces itself upon the mind, is the conviction that a 

 loaded wagon has been driven over the surface while in a yield- 

 ing condition; and a couple of grooves parallel to these, seen 

 for a part of the distance like the tracks of the second pair of 

 wheels, greatly confirms the illusion. 



The Island of Mackinac shows the most indubitable eviden- 

 ces of the former prevalence of the water, to the height of 250 

 feet above the present level of the lake; and there has been an 

 unbroken continuance of the same kind of aqueous action from 

 that time during the gradual subsidence of the waters to their 

 present condition. No break can be detected in the evidences 

 of this action from the present water-line upward for 30, 50 or 

 100 feet, and even up to the level of the grottoes excavated in 

 the brecciated materials of "Sugar Loaf," the level of "Skull 

 Cave" and the "Devil's Kitchen." 



While we state the fact, however, of the continuity of the 

 action during all this period, it is not intended to allege that 

 the water of the lakes, as such, has ever stood at the level of 

 the summit of Sugar Loaf. Nor do we speak upon the question 

 whether these changes have been caused hy the subsidence of 

 the lakes, or the uplift of the island and adjacent promontories. 

 It is true that the facts presented bear upon these and other 

 interesting questions, but we must forego any discussion of 

 them.* 



*Ab'in lint evi lonc:-s are famished along the shores of L.i'co Karon, of the unbroken con- 

 tinuity of the action of thos) physical fores which hive transported and assorted the mato- 

 riils of th; Drift. From the shingle beach form id by th : violence of the last gale, wo 

 trace ;i s;ri:s of beaches an 1 terraces, grain illy risiag as w-3 recede from the shore, and 

 becoming m>reanl in >re covered with th : linchens an I mo. ill and forest growths which 

 deeot: aatiqiity, until, in soma cases, the phenomena of shore action bl.-nd with tho 

 foitires wrhlch characterise the glacial drift. These observations t.illy so wjII with tha 

 vLws of Piet^t 0.1 the continuity of the Diluviin an 1 Molern Epochs, as cstiblished by 

 pi'.aei.itdogioit evidences, tnit 1 cmaot forb :ar referring tho reader to an article of his 

 whioh fills ual^r my notice as this r.-oert is gdig throigh the pr;s*. S^e BiLliotheqv* 

 Uniixrselli de tfenew," Vol. VIII., p. 255. Also, Sillitnan's Journal, [2 J XXXI, £45. 



