



SNOWBANK LAKE PLATE OP THE MESABI IRON RANGE, 1899. U. S. GRANT. 



all directions, illustrates one of the stages of transition from conglomeratic green- 

 stone to the gabbro. The fine clastic material is compacted and crystallized into a 

 rock which, in the field, appears like diabase, and in the field it was styled diabase. 

 In thin section (No. 499H) it shows, first of all, a large number of small uralitic 

 hornblendes. These lie in a finer matrix consisting of a confused mixture largely of 

 feldspar, but in which are fine particles that appear to be magnetite. The rock is 

 evidently the product of imperfect metamorphism of a fine basic debris. 



The iron ore south of Disappointment lake is structurally a part of the musco- 

 vadyte stage of the greenstone-gabbro transition, but whether a part of the Upper 

 or Lower Keewatin is uncertain. N. H. w. 



