L. C. Johnson — Grand-Gulf Formation of Gulf States. 213 



f Horn stein — variation of magnetic elements at Prague ) _. ... 

 Variation and St. Petersburg during 1870, \ 



of J Braun — variation of magnetic elements at Greenwich \ 



Magnetic and Makerstown during five years, between >• 24-18 



Elements. 1844 and 1870, 



\^Liznar — magnetic disturbances (storms), 24 - 29 



Photosphere \ Carringlon — from sun spots — seven years' observations, 24 - 97 



Equatorial values. } Sporer — ■" " " 24 - 60 



Wilsing — from faculse. 25 - 23 



Crew — by spectroscope, equatorial value, 26 - 23 



It will be observed that the lowest value by any one method 

 is higher than the highest of the next preceding. May this 

 not correspond to a physical fact, viz : that as we pass from 

 the more central portions of the sun, up through the photo- 

 sphere, faculse, and absorptive layer, there is a gradual decrease 

 of angular velocity ? 



Haverford College, April 16, 1889. 



Art. XXVIII.— The " Grand-Gulf" Formation of the Gulf 

 States ; by Lawrence C. Johnson. 



The group of clays, sands, sandstones and qnartzites called 

 the Grand-Gulf formation by Dr. Eugene W. Hilgard, has a 

 boundary as yet undefined in Texas and Louisiana, and is little 

 better known in the States east of the Mississippi River. Dr. 

 Hilgard considers it of fresh water origin, and upon good 

 grounds ; but of what precise age no one has been bold 

 enough to advance a definite opinion. Fossils are rare : a few 

 Uniones have been found, and in places, there are many leaf 

 impressions. It cannot be older than Miocene, and is as 

 certainly not Quaternary. 



The sandy clays, and quartzose sandstones of this formation 

 are so peculiar in structure, colors and general appearance that 

 they are easily recognizable, and cannot well be mistaken for 

 any other in these States, much less for any of the calca- 

 reous groups northward of it. By all observers it is agreed 

 that the strata next in this direction, are of Dr. Hilgard's 

 Vicksburg Formation. The trend of the northern boundary 

 of the " Grand Gulf " — from the vicinity of the place giving it 

 its name, in Claiborne County, Miss., is southeastward at such 

 an angle that at the Alabama line it has a breadth only half as 

 great as on the Mississippi River, that is : allowing an average 

 of twenty miles for the coast formations, it is about sixty 

 miles in width next to Alabama, against one hundred and 

 twenty-five on the meridian of Yicksburg. No critical 

 surveys of it having been made and its eastern extension is 

 only conjectural. 



Am. Jouu. Sci.— Third Series, Vol. XXXVIII, No. 225.— Sept., 1889. 

 14 



