Clayton — Six and Seven Day Weather Periods. 223 



to distinguish the one from the other. The three magnetic 

 lines, A, B and C, and the connection of two of them, the A and 

 the C, with characteristic and similar rocks, are facts not to be 

 doubted. Nor is it any less clear that the rocks of the A and 

 B lines, and of the B and C lines dip toward each other in the 

 respective spaces between them. There is no positive evi- 

 dence as to the nature of the B line rock, for no one has ever 

 seen it. Therefore the conclusion that the three lines repre- 

 sent the same rock is an inference which underground explora- 

 tion may prove to be erroneous. All that can now be said is 

 that of the five possible hypotheses of equivalence or non- 

 equivalence between the A, B and C rocks, that of equivalence 

 is by far the most probable. 



Assuming equivalence the evidence points then to these 

 conclusions : 



(1) The lower Menominee quartzite limestone and slates are 

 all older than any formation in the Marquette area. 



(2) The Michigamme jasper was deposited in a continuous 

 sheet over both districts, and in the Marquette constitutes 

 both the iron-bearing formation and, for most of the area, the 

 lower quartzite. 



(3) The principal ore horizon of the Menominee has no 

 equivalent in the Marquette district. 



Cambridge, Mass., Nov. 21, 1893. 



Art. XXII. — Six and Seven Day Weather Periods ; by 

 H. Helm Clayton. 



There is a seven day period in the weather, so noticeable at 

 times in the United States, that it has embodied itself in such 

 popular sayings as, " If it rains on the first Sunday of a month 

 it will rain every Sunday," etc. 



In regard to this period, as early as 1858, Prof. Joseph 

 Henry, Director of the Smithsonian Institute, wrote : . . . . 

 " Most persons can remember the occurrence in succession of a 

 series of storms on Sundays. In one case we recollect this to have 

 taken place six times in succession. There is nothing in this 

 particular day to induce the occurrence of a storm, but merely 

 it will be more likely to be remembered when it happens at 

 this time; and although the interval may not be precisely 

 seven days, yet it may differ so little from this that a part of 

 the first and sixth Sundays may be included in the cycles of 

 disturbance." See Patent Office Report, 1858, page 490. 



In a work on The Atmospheric System Developed (1870) 

 by Thomas B. Butler is found the following : " It is doubtless 

 within the recollection and experience of every one who has 



