356 THE PENOKEE IKOJiT BEARING SERIES. 



everything else adjacent. The rdcks have a strong soapy feel, and because 

 of this, and the fact that they are somewhat like rocks in other districts asso- 

 ciated witli iron ore, the miners have given them the name of soapstones. 

 These soapstones in this district never have the schistose structure and seri- 

 citic appearance presented by the soapstones of the Marquette, Vermilion 

 lake, and Menominee districts. This difference may be and, indeed, proba- 

 bly is, due to the fact that in the latter the rocks have been subject to pow- 

 erful dynamic forces. 



A microscopical study shows that in the less decomposed phases of rock 

 the character of the alteration is not materially different from that already 

 described as occumng in the diabases of other parts Of the series; that is, 

 the augite is merely altered to amphibole and the feldspar has been to 

 some degree affected by gray decomposition. In other cases the alteration 

 has resulted in the formation of green chlorite in the place of the augite, 

 the feldspar being affected"" the same as in the previous case. When the 

 decomposition has proceeded farther there appears quite often, in consider- 

 able quantity, a brilliantly polarizing material which is taken to "be a 

 zeolite. 



When the decomposition has gone very far even the magnetite is 

 mostly or wholly peroxidized. The place of the augite and feldspar is 

 largely taken by a colorless or pale yellow material. Between crossed nicols 

 this substance is often wholly dark or dull gray and does not change its 

 appearance by rotation. At other times it polarizes as an obscure aggregate 

 whose color and appearance are somewhat like those of sei'pentine, although 

 analyses indicate that that mineral is not present. In all but the most altered 

 ]iliases some chlorite and apparently a little secondary quartz are present. 

 Altundantly scattered through most of the sections are particles of limon- 

 nite, hematite, and sometimes magnetite. When the rock is so altered that 

 none of the original minerals remain, the diabasic structure frequently is 

 imprinted upon the homogeneous almost amorphous material. lu the some- 

 what rare extreme degree of alteration, however, all definite structure has 

 been obliterated, and such material, if examined by itself, gives no indication 

 whatever of its orig-in. That these soapstones are altered diabases is shown 

 by the facts: that in certain cases the same dikes exhibit little altered and 



