METHODS OF COKRELATION 459 



UNCONFORMITIES IN THE CAMBRIAN SANDSTONES AT ABLEMANS, 



WISCONSIN 



Two problems of this kind were solved this summer in Wisconsin. 

 Both related to early Paleozoic sandstones that had been confused. The 

 first instance was found at Ablemans, a noted locality to the west of 

 Baraboo, where an unusually hard and supposedly unfossiliferous Cam- 

 brian sandstone lies in sharply eroded old valleys in the Precambrian 

 Baraboo quartzite. A year ago I visited the large quarries at Ablemans 

 and decided that the sandstone filling the old valleys is of the age of the 

 Dresbach sandstone of Minnesota. Over this sandstone were remnants 

 of another sandstone formation that a short distance to the north is seen 

 to spread unconformably over the lower sandstone and the surrounding- 

 hills of quartzite. Its base is formed by a heavy bed of conglomerate, 

 composed almost entirely of perfectly rounded pebbles 2 to 6 inches or 

 more in diameter. Except that this upper transgressing sandstone forms 

 the base of the Ozarkian system in this region, it has no immediate in- 

 terest in this connection. I should add, however, that the identifications 

 made in the vicinity of Ablemans necessitated the assumption that the 

 Cambrian formations normally intervening in Wisconsin between the two 

 sandstones recognized here — namely, the Franconia sandstone, the Saint 

 Lawrence formation, and the Jordan sandstone — were absent here either 

 through nondeposition or pre-Ozarkian erosion. 



During the past winter I received notice that a number of specimens 

 of a brachiopod which were recognized as belonging to a species that till 

 then, and I am glad to add even today, is thought to be confined to the 

 lower fourth of the Franconia formation, had been found in the sandstone 

 which I had identified as Dresbach. As might be supposed, this infor- 

 mation proved somewhat disquieting. If my judgment was wrong, the 

 way to benefit by the experience was to see the facts for myself in the 

 field. Accordingly, in June the State Geologists, Mr. Hotchkiss, and his 

 assistant, Doctor Weidman, accompanied me to Ablemans. 



Well, it required little more than one hour to satisfactorily explain the 

 difficulties. The quarry in which the Franconia fossils had been found 

 was the first to be visited. Its face exceeds 100 feet in height. The 

 greater lower part of this quarry face, on close examination, again seemed 

 to me surely Dresbach. Then it was learned that the fossiliferous bed is 

 near the top of the quarry. Not to weary you with details, I shall state 

 the crucial facts at once. Just beneath the fossil bed a suspicious contact 

 was observed, which, on being traced around the quarry, proved to be 

 irregular, and at one place very much so. Moreover, touching or lying 

 on this uneven plane we found boulders of Baraboo quartzite, moderately 



