1>. White — Cretaceous Plants from Martha's Vineyard. 93 



field as it would be but for the presence of the pipes; these 

 lines are Bhown in tig. 3. 



Here are clearly shown four distinct disturbances : — (I) That 



in the S. E. corner of the wing which was at once attributed to 



I pair of steam pipes at F, nine feet, from the eastern wall of 

 the wing and reaching from the basement to the third floor, 

 which had been overlooked until pointed out by this system of 

 lines. (2) That in the N. W. corner due to the stove ahove G 

 as before described. (3) That in room 13, which might he pro- 

 duced by a horizontal magnet above or below the point K with 

 its north pole directed toward the north. Search showed the 

 probable cause in the presence on the second floor of a heavy 

 iron table top four feet long, two feet wide and an inch thick, 

 whose position is indicated in tig. 3. (4) A disturbance in 

 rooms 15 and 16 which has not been traced to its source. 



The foregoing account contains the substance of a paper read 

 before the Mathematical Physical Club of Boston and Cam- 

 bridge. May, L887. I had hoped to extend the observations 

 and especially to investigate the last mentioned disturbance in 

 rooms 15 and 111 It is only within the last month, however, 

 that I have again taken up the subject and have been able to 

 show that the brick piers have a sufficient amount of free mag- 

 netism to produce the observed effect. These results I shall 

 make the subject of a future paper ; meanwhile the present 

 writing will serve to show the magnitude of the disturbance 

 which may arise in practice from such common objects as stoves 

 and iron pipes. 



Jefferson Physical Laboratory, Xov. 1889. 



Art. XYI. — On Cretaceous Plants from MarthcCs Vineyard; 

 by David White.*— With Plate II. 



It is remarkable that, although the existence of fossil vege- 

 table remains on Martha's Vineyard has been on scientific 

 record for nearly one hundred years, and the announcement, 

 accompanied by several figures, of the occurrence of dicotyle- 

 donous leaves at Gay Head was made in the report of the State 

 Geologist of Massachusetts over sixty years ago, no one has 

 ever made a systematic study of the entombed plants, nor 

 attempted to draw any evidence therefrom as to the age of the 

 containing strata. No one seems ever to have searched there 

 for plants with that object in view. The probable reason for 

 this is the lack of importance which they had in the eyes 

 of the State geologist, as well as the crude and indeterminate 



* Published with the permission of the Director of the U. S. Geological Survey. 



