PLATE LXXXVIII. 



THE DULUTH PLATE, 1S1MJ. N. H. WINCHELI, 



The best synopsis that- can be given of the geology represented by this plate is 

 probably that which is derived from the record of the deep well, sunk for gas, at the 

 Short Line Park station a few years ago. 



1. Previous to reaching the depth of 231 feet no drillings were preserved, but 

 this interval is supposed to have been occupied by red sandstone and shale like that 

 seen in the river banks adjacent, perhaps with more or less of eruptive material, 

 231 feet. 



2. The first drillings preserved are of eruptive nature and this rock becomes 

 amygdaloidal trap, or surface lavas. There is then an interval of 104 feet not repre- 

 sented by drillings, supposed to be occupied mainly by eruptive strata, but probably 

 embracing also fragmental materials, such as reddish conglomerates and sandstones, 

 erosion products of cotemporary eruptions. Below this uncertain interval, as well 

 as above it, was rock which was plainly a surface eruptive. If these all be put 

 together we have, eruptives and surface flows, 217 feet. 



3. Below these eruptives follows a series of hard quartzytes and quartz con- 

 glomerates, with but little eruptive material, having a thickness of forty-eight feet. 

 The striking similarity of this to the pyritiferous white quartz conglomerate seen in 

 the left bank of the St. Louis river, a little west of Short Line park, leaves no alter- 

 native but to parallelize it with that rock. But here, instead of lying on the Thom- 

 son slates, it lies on another series of eruptives. Hence, quartz conglomerate and 

 quartzyte, 48 feet. 



4. These lower eruptives are amygdaloidal, and resemble greatly those seen at 

 Duluth and eastward to Chester creek, and ft seems necessary to parallelize them 

 with the flow rocks at Duluth, 91 feet. 



5. Below this second series of eruptives is found the Thomson slate, the sup- 

 posed equivalent of the Animikie. This formation, although penetrated by the drill 

 to the bottom of the well 1,5174 feet below the natural surface, was not pierced at 

 that depth. These parts may be put together succinctly as follows: 



1. Fond du Lac red sandstones and shale. Potsdam, - 231 feet 



2. Surface eruptives, Manitou, Potsdam, 217 " 



3. Pyritiferous cjuartzyte and quartz conglomerate, Puckwunge, Potsdam, 48 



4. Surface lavas, as at Duluth, Cabotian, 91 " 



5. Thomson slates, Animikie(?), - 930^ " 



Total, - 1,517J feet 



It is to be noted that the Fond du Lac sandstones are chronologically separated 

 from the coarse pebbly conglomerate on which they lie at the river by a series of 



