﻿O. T. Sherman — Spectrum of Comet C, 1886. 157 



of the Keweenaw land. When Keweenaw land is spoken of r 

 I refer to that formed of the strata of the Keweenaw system 

 and the Archean rocks with which it was associated. 



Before the Keweenaw land was depressed the Middle Cam- 

 brian fauna passed through or around the barriers between the 

 Atlantic and western seas, and, as the Keweenaw land was dis- 

 appearing beneath the waters, the Upper Cambrian fauna 

 spread over the area occupied by it and left its record to aid 

 us in fixing the geologic date of the submergence of the 

 Keweenaw land and to explain the absence of the Paradoxides 

 or Atlantic fauna in the early Cambrian strata of the western 

 side of the Continent. In the diagramatic section (fig. 9), I 

 have endeavored to show the relations of the Potsdam or 

 Upper Cambrian to the Keweenaw land. 



The evidence of the existence of the Keweenaw land is both 

 stratigraphic and paleontologic. That life existed in the seas 

 at the time of the deposition of the sediments of the Keweenaw 

 system, is shown by its presence in the Chuar formation of the 

 Grand Canon series. 



It may be urged that there is too much theorizing, on insuffi- 

 cient data, in the preceding statements, but, while waiting the 

 accumulation of evidence it is well to have a working theory 

 and as such the " pre-Cambrian Keweenaw land " is proposed, 

 and the fragmentary remains, less the Archean portions, called 

 a "pre-Cambrian Paleozoic System." 



Art. XVIL— Note on the Spectrum of Comet C, 1886 ; by 0. T. 



Sherman. 



Comet C, 1886, presents to telescopic view, a faint oval of light 

 about one and a half minutes in diameter. In the north pro- 

 ceeding quarter is a poorly defined condensation. Although 

 well situated for observation, it is yet not especially suited for 

 spectroscopic analysis ; still out of curiosity the equatorial of 

 the Yale Observatory was turned thereon. The result is not 

 without interest : no less than seven loci of light present them- 

 selves, where three are usually seen. 



On account of the circumstances it is necessary to de- 

 scribe somewhat in detail the apparatus and mode of ob- 

 servation. The comet's light focused upon the plane of the 

 slit by the object glass of the equatorial (8 in.), and passing 

 through the collimating lens falls upon a Rowland's flat grating, 

 14,347 lines to the inch, and is then focused for observation 

 by a small telescope with low power eye- piece. The grating is 

 fastened to an arc moved by a tangent screw, allowing the 



