216 Scientific Intelligence. 



While many other species presented minor features of inter- 

 est, their description would enlarge this paper beyond its scope. 

 Briefly stated, in conclusion, in this overturned series the sand- 

 stones, conglomerates and shales are undoubtedly of older age 

 than the limestones, but I am not inclined to assign them to 

 any definite formation, out of consideration of their isolation. 

 They may be more or less nearly equivalent to the Medina 

 beds as exhibited in the Shawangunk Mts. The limestones 

 immediately overlying, are without doubt equivalent to the 

 Water-lime division, and these are in turn overlaid by lime- 

 stones carrying a mixed Pentamerus and Delthyris-shaly fauna, 

 the uppermost members of which in their southern extension 

 are superficially decomposed and impregnated with iron ores, 

 and they contain an abundant fauna, including some species of 

 lower divisions, together with some formerly restricted to 

 higher horizons. 



The relations of these formations to others in the district 

 will be discussed in a subsequent paper. 



Finally the writer wishes to acknowlege his great indebted- 

 ness to Professor P. P. Whitfield for his kindly aid and advice, 

 without his assistance many of the more obscure species would 

 not have been recognized. To Professor Hall I am likewise 

 indebted for aid in the determination of obscure forms and for 

 other favors. 



To my aids, Messrs. F. Marshall Smith and Wolcott Foster, 

 I am also under obligations. 



"Washington, D. C. 



SCIENTIFIC INTELLIGENCE. 



I. Physics and Chemistry. 



1. On the Dilatancy of Media composed of rigid particles 

 in contact. — Notwithstanding the many hypotheses of matter, it 

 does not appear that any attempts have been made to investigate 

 the dynamical properties of a medium consisting of smooth hard 

 particles held in contact by forces transmitted through the me- 

 dium. Osborne Reynolds has pointed out the existence of a 

 singular fundamental property of such granular media, which is 

 not possessed by known fluids or solids. To this unique property 

 of granular masses he gives the name " dilatancy" because the 

 property consists in a definite change of bulk consequent on a 

 definite change of shape or distortional strain ; any disturbance 

 whatever causing a change of volume and generally dilation. In 

 the case of fluids, volume and shape are perfectly independent. 

 But with granular media, the grains being sensibly hard the case 



