DIRECTIONS OF SLOPES 671 



The Palms quartz slate is a shallow-water deposit with ripple-marks 

 nearly parallel to the present strike, but pitching down to the east a few 

 degrees. These ripples have been interpreted as possibly being parallel 

 to the shore. Which way this shore lay — to the north or south — is not 

 indicated. Its uniform thickness over most of its area and rapid thicken- 

 ing at the east indicates a bottom that was level and sinking at a uniform 

 rate except at the east end, where the sinking was more rapid. 



The Ironwood formation, by its parallelism to the Palms, indicates a 

 continuation of Palms conditions as to slope of bottom, with probably 

 a more general tilting to the east indicated by tlie gradual thickening of 

 the formation in that direction. 



The Tyler slate (and graywacke) was preceded by some erosion, but 

 wherever observable its lower beds are essentially parallel to the Iron- 

 wood. Its character indicates a gradual sinking of the bottom and a 

 fairly rapid accumulation of the sediment in relatively shallow water. 

 Whether its thick middle and thin ends are due to more rapid sinking 

 of the middle and consequent thicker deposition or to deposition of a 

 uniform thickness and later erosion is not known, but it is probably due 

 to both. At any rate, the general axis of the basin must have been nearly 

 parallel to the present outcrop. The shore may have been either to the 

 north or south so far as evidence from the formation is known. 



The Lower Keweenawan sediments have not been studied sufficiently 

 to be sure from which direction they came. Such evidence as we have is 

 slight and conflicting in character. The flows give much better evidence 

 with few conflicting features. In a quarry in the base of the flows north 

 of Ironwood the second flow advanced over a thin mud deposit and 

 squeezed it up before it in such a manner as to indicate that the flow 

 advanced from a northerly direction. 



A second line of evidence is the fanning of the dips. The flows at the 

 south are much steeper than those at the north in practically every known 

 section. This can be explained as the normal decrease in dip of the beds 

 toward the middle of a normal compression syncline. It can equally well 

 be taken as an indication of flows thickening away from the source to fill 

 a sinking syncline, but this implies a source outside the syncline for which 

 good evidence is lacking. It is believed that the flows thinned away from 

 the source in normal fashion and that this thinning up the present dip 

 indicates a source now concealed down the dip. 



A third line of evidence for the direction of movement of the flows 

 was seen with Graton and Butler and their associates this past summer 

 in the Calumet and Hecla mine. Here the bottom of the flow that cov- 

 ered the Calumet and Hecla conglomerate showed a great number of 



