ELKHEAD MOUNTAINS. 173 



from the same locality, a rock of somewhat similar appearance, shows, 

 together with the great number of large glassy quartz grains, a few sani- 

 din crystals and a large proportion of brown biotite plates scattered 

 through the mass. Under the microscope, considerable augite is seen, but 

 no hornblende or olivine. These spurs were so densely wooded that it was 

 impossible to determine the relations of these different flows of volcanic 

 rock, but the occurrence of a well-defined basalt on the northern spur of 

 Hantz Peak would seem to indicate that this series of rocks marked a 

 gradual transition from the more acid trachytic flows to this final basic 

 outburst, along the contact-line of the volcanic flows with the Archaean body. 

 The Hantz Peak basalt body occurs on a densely-wooded ridge, running 

 out to the northeast from this peak, in which few rock-outcrops are visible. 

 The rock itself is a dark-blue, compact mass, rich in olivine, in which 

 a few scattered crystal of plagioclase-feldspar could be detected. In this 

 basalt, the microscope detects the presence, besides olivine and plagioclase, 

 of augite, biotite, and apatite, while that of nepheline, though not distinctly 

 recognized, is confirmed by the general resemblance of this rock to the 

 nepheline-basalts found to the west, particularly at Bastion Mountain. 



Hantz Peak is the highest and most prominent point in this region. 

 Its summit is a very sharp cone, whose slopes to the south and east are 

 extremely abrupt, falling off at an angle of nearly 40°. On the north 

 shoulder of Hantz Peak, about 300 feet below the summit, is a remnant of 

 sedimentary beds, consisting of horizontally-stratified sandstones, which 

 have been much metamorphosed, and, in some cases, completely vitrified. 

 Within these sandstones is a development of a fine-grained conglomerate, 

 made up of small pebbles of black and greenish chert and jasper, which is 

 quite identical with the characteristic and 23ersistent conglomerate, which 

 we find throughout this region at the base of the Dakota Cretaceous. For 

 this reason, and from the fact that to the east of Hantz Peak, in contact 

 with the Archaean rocks, is a small development of Triassic sandstone, 

 these quartzites or sandstones have been referred to the Dakota group of the 

 Cretaceous. 



The trachyte which forms the main mass of Hantz Peak is a mauve- 

 colored rock, which separates easily into sherd-like laminae. It shows 



