Geology and Natural History. 71 
9. Upon the Electro-magnetie rotation of the Plane of Polari- 
zation in Gases.—Kunpt and Koénteen state as the result of their 
oS se faa the following: 
The amount of this rotation under like conditions is different 
for Ps different gases. 
They detail the precautions employed in their research, and give 
the methods at length. It is found that the elec ctro-magnetic ro- 
tation is the greater the greater the index of refraction of the gas, 
although the authors have not been able to determine the exact 
south-direction would experience under the magnetism of the earth 
a rotation of 1°.— Wiedemann’s Annalen der Physik und —* 
No. 10, 1879, p. 278. 
iE. pint AND —— History. 
E (From a letter to J. D. Dana, dated Philadelphia, 
Dec 9.)—Professor Lesquerenx has just tags Butho- 
trephis foliosa on a slab of roofing slate from the rries on the 
Susq nna River near he aryland line. This i is a most im- 
portant discovery. Professor Frazer has been studying the roofing 
slate belt and adjoining chlorites, for several years in connection 
with his York and Lancaster county work. He never found an 
traces of organic life, nor could hear of any. But he found hee 
curious forms in the rocks across the state line in Ma aryland, one 
of which tacked like a flattened Orthoceras. Bagh saa cree 
Hall a and Mr, fa hitfield were disposed to con 
lety’s Prosestings and for the Reports of ‘the Surv: e 
are the only fossils ever seen in that region to oat knowledge 
e sl 0 ue is. in our museum an 
re 
limestone, ghd in the Hudson hivoe slates, one in the Clinton. 
he is reported from the Devonian of Russia. Several from i 
sub-Carboniferous remain Gustadied. B, foliosa is characterist 
