786 THE GEOLOGY OF MINNESOTA. 



[Greenstone. Esterellyte . 



and hornblende, with another feldspar species. There may have been an accession 

 of acid matter or such elements that the whole tone and tendency of the magma in 

 consolidation was altered, resulting in a rock quite different from that which would 

 have been produced had no such change supervened. Rock like this is found at 

 Vermilion lake, in form of dikes. (Compare Nos. 872 and 877. Also compare No. 2102.) 

 However, the appearance of this rock is that of one crystallized from a debris 

 rather than from a magma. N. H. w. 



No. 1787. GREENSTONE. 



"Amygdules, or pipe-like tubes, in the boulders or bombs of the agglomerate at Ely, filled with silica, 

 which appears to be 'chalcedonic' or minutely granular. This new feature is found sparsely in the rock toward 

 the southwest from the cut at the railroad already described." 



Ref. Annual Report, xxii, page 5. Compare Nos. 1510 and 1511. 



Meg. Specimen lost. No section. 



Age. Archean (Keewatin). u. s. G. 



No. 1788. GREENSTONE. 



Southwest from the railroad cut at Ely, toward the Lockhart property, this rock abuts against a bouldery 

 mass of the graywacke, or agglomerate, and its grain and substance seems to enter the bouldery mass, and to 

 surround the bombs, at the same time becoming finer, forming the dark -green scale which envelops them. 



Ref. Annual Report, xxii, page 5. 



Meg. When collected this was considered a representative of the rock No. 1786. 



Mic. It may be a representative of that rock, but it is much more decayed, 

 showing a considerable calcite. There are no porphyritic hornblendes, but a fine and 

 often fibrous actinolite or other amphibole is abundant, especially in the areas of the 

 old pyroxenes. There is also a wide distribution of small, irregular grains of epidote 

 like those mentioned in the description of No. 1786. There are multitudes of little 

 feldspars, much smaller than in No. 1786, and there are remnants of old feldspars 

 now mostly occupied by a micro-granulitic mass of fresh feldspar grains, the original 

 orientation being sufficiently preserved, in some cases, to show the change that has 

 taken place. A small amount of quartz can be seen to surround, occasionally, the 

 small epidotes. Two sections. 



Age. Archean (Keewatin). 



Remark. If this is a representative of rock of No. 1786, and if that be camp- 

 ton yte, then camptonyte is not entirely a dike rock. Again, this rock is quite similar 

 to much of green rock which has been included under the name greenstone, and is 

 allied to the tuffaceous greenstones. N. H. w. 



No. 1789. ESTERELLYTE(?) 



About three-fourths of a mile west of Ely. 

 Ref. Annual Report, xxii, page 5. 



Meg. A knob rising irregularly in the midst of the greenstone, presenting a 

 nearly white color, contrasting with the dark tint of the greenstone. It extends 



