76 THE CRYSTAL FALLS IRON-BEAKING DISTRICT. 



liip-lily probable that this sUite in an extremely plicated couditiou may 

 underlie the volcauics of this area, and it is so represented in section G-H, 

 Plate VI. As evidence of this, in T. 43 N., E. 31 W. the volcanics 

 overlie the Mansfield slate iinconformably. 



In places test pits have disclosed an amygdaloidal lava flow immedi- 

 ately overlying the Mansfield slates. At one place, at the northeast corner 

 of sec. 7, T. 43 N., R. 31 W., angular fragments of the underlpng black 

 slate have been found in the tufaceous deposits of the Hemlock volcanics. 

 Farther south, along the contact just west of the Mansfield mine, a con- 

 glomerate is exposed, which contains fragments of slate, lava, and rounded 

 grains of quartz with secondary enlargements. The rock is e^ndently 

 water deposited. There is also obtained from the workings of the mine a 

 conglomerate, taken from just above the ore, which consists of lava frag- 

 ments and pieces of chert and ore, as mentioned on pp. 64, 68. From these 

 occurrences it is clear that some of the sedimentaries are unquestionably 

 older than some of the volcanics, and yet the conglomerates bearing the 

 fragments of ore and slate contain also fragments of lava, showing the 

 existence of some of the volcanics before the deposition of this conglom- 

 erate. The only explanation of all of the facts which has occurred to me 

 is as follows: After the ore-bearing Mansfield slate was deposited, an erosion 

 interval occurred. Then followed a volcanic outbreak. It is highly 

 probable that this outburst began far north of the Mansfield mine, coincident 

 with the upheaval which resulted in the erosion of the Mansfield slate. 

 The volcaific ejectamenta were mixed with the sedimentary fragments and 

 all together were rounded and bedded, forming in places conglomerates. 

 In places along the shore lava flows descended, some reaching into the sea 

 and coA'ering the sedimentaries along the shore where no conglomerate had 

 been formed. At other places deposits of scoriae, etc., including fragments 

 of slates from the sedimentaries through which the volcano burst, were 

 made, and thus deposits of tuff are found overlying the sedimentaries. 

 The various deposits, though really separated by a slight physical break, 

 are practically conformable with the series below, all liaAang a north-south 

 strike and a high westward dip. 



The formations which underlie the volcanics in the northern and 

 southern parts of the district are of difi^erent character. This difterence 



