HISTORICAL REVIEW OF THE GEOLOGY OF MICHIGAN. 185 



Desor ou surface geology and James Hall on the paleontology and sedi- 

 mentaries, and also by Burt and Hubbard of the Michigan Survey and 

 Williams, Stevens and Hill. Let us compare the amount of information 

 attained at this date. The broad bands of sedimentaries in the eastern 

 half of the Upper Peninsula sweep around substantially as they do on 

 my latest map. No finer subdivisions have been made in the sedimen- 

 taries and no material error has been corrected with the one exception 

 that the upper Helderberg of the Devonian System is extended mucli too 

 far north. Passing to the pre-Cambrian rocks we find the great range of 

 copper bearing rocks, which, by the waj', were then classed with the 

 Silurian, extending from Keweenaw Point to the Wisconsin line and 

 dipping towards Lake Superior and re-appearing on the other side of 

 Lake Superior in Isle Royal where they dip to the southeast. The rocks 

 prior to the copper bearing rocks are divided into crystalline schists 

 and granite, corresponding roughly, but with fair distinctness with the 

 Laurentian or Basement complex and the Huronian or Lower Algonkian 

 of later writers. The main questions left, which were not altogether 

 settled to the entire satisfaction of everyone, are as follows : What are 

 the relations of the red sandstones which appear both to the northwest 

 and southeast of the Keweeuawan Copper Range and how nearly are 

 they the same? What are the mutual relations of the sedimentary and 

 igneous rocks associated in the Azoic system, which Dana later called 

 Archean, and what are the details of the stratigraphy? The geology of 

 the Upper Peninsula as left by Foster and Whitney' was as well or better 

 known than that of the Lower Peninsula, and its mineral wealth at- 

 tracted the attention of the mining men of Europe. Fr. C. L. Koch' gave 

 an account of his trip and a map, which though based upon Foster and 

 Whitney, gives considerable more detail in some parts and gives a more 

 accurate petrographic description of the melaphyres or traps and amyg- 

 daloids of the copper bearing rocks. Rivot," a French geologist, also 

 made a trip but the observations of these geologists had little effect on 

 the course of progress for they were overlooked and rediscovered inde- 

 pendently by later writers. 



With the revival of the Geological Survey under Alexander Winchell 

 interest and progress is shifted to the Lower Peninsula and his report,' 

 issued in 18G1, contains a clear and generally accurate account of the 

 general stratigraphy of the Lower Peninsula, with a mass of further 

 information regarding the occurrence of coal and salt. Though this 

 report contains no geological map. it should be read in connection with 

 the articles* on Michigan and the maps prepared therewith, which he 

 prepared for the Walling-Tackaberry Atlas, issued in 18G4-5, 1S66, 1873. 

 By this time the general outline of the Coal Basin had been determined, 

 and the general basin-like structure and the principal horizons of the suc- 

 cession of rocks beneath. The only thing that can be said in a general 

 criticism is that the thickness of the various formations was uniformly 

 underrated. One point occupied Winchell's time and attention for a 

 number of years and a series of papers," and, that was the Marshall Group. 

 The state of affairs is about as follows : New York was the first State 

 in which the Paleozoic column was thoroughly worked out in detail and 

 it has been used as a norm by geologists of other States. In that State 

 we find, beginning at the base of the upper Devonian with a black shale, 

 a series first of blue shales, then of fine-grained bluish and greenish 

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