452 SCIENTIFIC RECORD FOR 1883. 



some few organic forms, as yet undescribed, which lead Walcott to 

 regard this lower series, lying between the Tonto group and the crystal- 

 line rocks below, as also of Cambrian age, though they had previously 

 been regarded by Powell as pre-Cambrian. These rocks, judging from 

 the collections seen by the writer, are wholly uncrystalliue sandstones and 

 shales, unlike the Taconian in character, and it is suggested by Wal- 

 cott that they may correspond to the Keweenian, which occupies a po 

 sition between the Taconian and the Potsdam, being separated from thifc 

 latter by a great unconformity and vast erosion. The Keweenian, more 

 over, as the writer has shown, presents evidences of organic forms. 

 Until, however, these rocks of the Grand Canon and of the Keweenian 

 series shall have been found to include the representatives of the first 

 fauna of Barrande it would be unphilosophical to include either of them 

 in the Cambrian. Few thoughtful geologists now suppose this fauna to 

 mark the dawn of organic- life, and we may hope to find beneath its 

 horizon a long series of organic forms stretching far backward through 

 what have been aptly termed the Transition rocks to those of the Primi- 

 tive time. 



The great series of silicious and argillaceous rocks, with some in- 

 cluded limestones and beds of crystalline iron ores, found to the north- 

 west of Lake Superior, which were provisionally designated by the pres- 

 ent writer as the Animikie series, have since been studied by N. H. 

 Winchell, in Minnesota, and found to have a thickness of not less than 

 10,000 feet. These rocks, which underlie the Keweenian, are, in the ab- 

 sence of these, unconformably overlaid by the horizontal Cambrian 

 sandstones of the Mississippi area, as is well seen on the Saint Louis 

 Eiver, in Minnesota, and have been by the writer referred to the Taco- 

 nian. They have lately yielded him the remains of an organism believed 

 to be a sponge. The Keweenian series itself in places rests upon these 

 rocks, as elsewhere upon the Huronian, the Laurentian, and at Duluth, 

 upon rocks which have been referred by the writer to the Norian series. 

 He has suggested that, as long since claimed by Emmons and Hough- 

 ton, some of the iron-ore-bearing rocks of northern Michigan belong to 

 the Animikie or Taconian series, although hitherto confounded with the 

 Huronian rocks of the region, with which both here and in the Atlantic 

 belt they have certain resemblances. 



The Cambrian rocks along the eastern side of the Atlantic belt, as 

 seen in Newfoundland, New Brunswick, and Massachusetts, present 

 an important field for comparative study. W. S. Dodge has lately re- 

 examined these rocks, as seen in the latter region. The argillites and 

 conglomerates of the Boston basin, as has long been known, afford at 

 Braintree a Cambrian fauna, which has been referred to the Menevian 

 horizon. It is there found abundantly in argillite beds, which dip with 

 a high angle to the south, and have a maximum thickness of 500 feet. 

 Their precise relation to the conglomerates of the region is left undeter- 

 mined. These strata are traversed both by feldspathic and by pyrox- 



