Association of American Geologists and Naturalists. 103 



quire a polarity contrary to that of the earth, thus diminishing in a sen- 

 sible degree the effect of terrestrial magnetism in the neighborhood. 



Prof. Locke also announced the fact that the point of greatest mag- 

 netic force- is at or near Lake Superior. Thus there are three impor- 

 tant poles or points nearly on the same meridian, nearly equally distant 

 from each other, and directly north of the United States, being between 

 the longitudes 85 to 90 : first, the true north or astronomic pole ; sec- 

 ond, Ross's pole of perpendicular dip, and of magnetical convergence, 

 twenty degrees south of the astronomic pole ; third, the pole of maxi- 

 mum intensity of magnetic force, 21£° south of Ross's pole, 424° south 

 of the north pole, viz. in 47£° of norm latitude. 



Prof. L. added that he had made a journey to Europe and purchased 

 the instruments for this research at his own cost ; that he had travelled 



ON 



investigat 



wn cost ; that now he has developed so many points of what seems to 

 him to be a regular system of magnetism in the United States, that he 

 feels almost irresistibly impelled to prosecute the subject, but the econ- 

 omy of his domestic affairs renders it inconsistent with his duty. 



Prof. Johnson presented an invitation from Lieut. Gilliss to 

 visit the Naval Observatory this afternoon at 5 o'clock, which 

 w as accepted. 



The President presented the invitation of Capt. Wilkes to 

 visit the collections of the Exploring Expedition at the Patent 



ce > and also to visit him at his residence on Saturday eve- 

 ni ng, which was accepted. 



Th 



ot the valley of the Connecticut River, with inferences as 

 tte relative age of the Trap and Sandstone," with illustrations. 



e ^ap tufa is a peculiar rock of volcanic origin, differing from 



^on trap in being conglomerated, or taking round pebbles into its 



position, and being stratified. It also contains one marked exam- 



a vegetable petrifaction, appearing like organic remains in igne- 



th r ^ Ut * >ro *' **' e »deavored to show that it was produced before 



ain ridges of trap along Connecticut river, by precursory outbursts 



P mice, scoria, ashes and melted matter, flowing over the bottom of 



en oc ean, and mixing with the sand and gravel, and so becoming 



°r less stratified, and enveloping: animals and plants. After this, 



tra sanc| stone accumulated over it, and finally the main ridges of 



^P v-cre protruded through the strata, tilting them up. Hence this 



nectic COnStilUting EaSt and Wcst Roc t and the Han S in S Hil]s in Con - 

 0r j ■ ■ . ' an " Holyoke and Tom in Massachusetts, was the one of latest 



m tllat valley — a point which had not before been determined. 



