"282 Cryptozoon Minnesotense at Northfield — Chaney. 



first dome. In the second form the layers of each structure seem 

 to terminate 





'X' 





sharply at the 

 line of junction. 

 Fig's. 6 and 7. 

 So far as 

 can be learned 

 from study with- 

 out microscopic 

 •examination the 



central portion ^^^,^ Q & l, snowing further structural features, possibly 

 of each dome is Cryptozoon. 



finely laminated with occasionally a lacuna between the laminae. 

 Across these lacunae there extend frequent calcareous filaments. 

 The outer layers as before stated are thicker and the cellular spaces 

 larger. In a few instances it has been possible to view horizontal 

 sections of these structures. At a point about a mile west of Dun- 

 das, Minn., I found such a case and was able to confirm the conclu- 

 sions drawn from the vertical sections. The size of these domes 

 varies considerably, the smaller ones being two feet along the base 

 and eighteen inches high, the larger reach ten feet in horizontal 

 dimensions and six feet in height. 



" With this statement of facts some discussion of the origin 

 of these remarkable structures may be undertaken. 



Three views are possible. 1st. They are entirely organic; 2nd. 

 They are entirely concretionary, huge inorganic masses; 3rd. 

 They are concretions formed about an organic core of relatively 

 small dimensions. 



In the fourteenth annual report of the Minnesota geological 

 survey are described and figured specimens of cryptozoon found 

 near Northfield and Cannon Falls. The figure is from a large 

 specimen some sixteen inches across, which is in the general 

 museum of the University of Minnesota. Similar specimens of 

 even larger size were found in grading a street in Northfield and 

 are now in the cabinet of Carleton College. Smaller specimens 

 have been found in considerable numbers. The figure in the re- 

 port just named shows the same general structure above described. 

 The microscopic structure is shown to be finely laminated, the 

 laminae being wavy. It is found that by patient digging there 

 may be extracted from some of the domes a central mass having 



