252 THE MARQUETTE IROX-BEARING DISTRICT. 



may have marked a time when subsidence had ceased and the Hmestoue 

 had been built upward until the finer-grained mechanical sediments could 

 be carried by the waves. That this is probable, rather than that the sea 

 had deepened so much as to make the limestone formation im])ossible, is 

 indicated by the fact that above the Wewe slate follows the Ajibik quartzite, 

 a coarser mechanical sediment. 



THICKNESS. 



As a consequence of the complicated folding of the district, it is exceed- 

 ingly difficult to give an accurate estimate of the thickness of the Kona 

 dolomite. It doubtless varies much, perhaps reaching its ma.ximum some- 

 where near the central part of the area, and thinning out in passing to the 

 west. South of Mud Lake the formation has an almost continuous exposure 

 for 1,500 feet, with a dip to the south varying from 78° to 90°. If there 

 were no minor folds, and calling the average dip 80°, this would correspond 

 to a thickness of about 1,375 feet. However, it is certain that just to the 

 north of this lake the slates are in a series of sharp isoclinal folds; and 

 that this is true for the dolomite, to some extent at least, is more than pos- 

 sible. How nuich this maximum thickness should be decreased on account 

 of this uncertain element of the problem it is difficult to estimate, but it is 

 wholly possible that the thickness as above calculated should be reduced 

 one-half At Goose Lake, as has been said, there is a continuous exposure 

 of the formation for a considerable distance. Here the thickness of the 

 layers was carefully measured and found to be 225 feet, with a possible 

 error of 25 feet. If the formation is supposed to have the same dip to the 

 northwai'd for the remainder of the detached exposures along the east shore 

 of Goose Lake, this amount may be increased by 150 or 200 feet. 



West of Tigo Lake the formation is exposed almost continuously for a 

 distance of 1,300 feet. The dip here varies from 25° to 40°, averaging per- 

 haps 30° or 35°. Calling the average dip 30°, this would give a thickness 

 of 650 feet. Although the limestone occupies an area as broad as 2 miles 

 in certain places, it can not be asserted, on the present information, that the 

 maximum thickness of the limestone is more than 700 feet, although it may 

 be twice this amount. 



