72 Geological Society : — 



And it follows that when (.r', y', z') is a point on the cubic, the 

 equation U=0 of the cubic may be written in the form 



sn-sp=o, 



an equation which is the basis of the subsequent investigations of the 

 paper. The autlior refers to a communicatiou to him by Mr. Cayley, 

 of an investigation of the equation of the conic passing through five 

 consecutive points of the cubic, in the case where the equation of 

 the cubic is presented in the canonical form x' -\- 1/' + z' + 6Lv)/z=0, 

 and lie shows that by the help of tlie above mentioned identity, the 

 investigation can be effected with equal facility when the equation 

 of the cubic is presented in the general form ; and he establishes 

 various geometrical theorems in relation to the conic in question. 

 Finally, the author considers an entirely new question in the theory 

 of cubics, viz. the determination of the points of a cubic, through 

 which it is possible to draw an infinity of cubics Jiaving a nine-point 

 contact, or complete osculation, with the given cubic. It is shown 

 that the points in question are those which are their own third 

 tangcntials, and this suggests the consideration of the new canonical 

 form, x'i/+y'c-\-~''x+2mxi/z^0, of the equation of the cubic; this 

 inquiry, however, is not pursued in the paper. 



GEOLOGICAL SOCIETY. 



[Continued from vol. xvi. p. 4/8.] 



December 15, 1858. — Prof. J. Phillips, President, in the Cliair. 



The following communications were read : — 



1 . " On the Succession of Rocks in the Northern Highlands." 

 By John Miller, Esq. Communicated by Sir R. I. Murchison, 

 V.P.G.S. 



Mr. Miller in this communication explained the history of our 

 knowledge of the geology of this district ; and, having given in 

 detail an examination that he made of the coast last autumn, he 

 drew particular attention to the faithful and comprehensive descrip- 

 tions of the Old Red district by Sedgwick and Murchison in former 

 years, and showed that his own observations quite coincide with the 

 results of Sir Roderick Murcliison's late correlation of the Gneissic, 

 Cambrian, Silurian, and Old Red strata of the coasts of Sutherland, 

 Ross-shire, and Caithness. 



In conclusion, Mr. Miller pointed out that the Durness Limestone 

 and the fossiliferous beds of Caithness were still open fields for 

 careful and energetic explorers. 



2. " On the Geological Structure of the North of Scotland. 

 Part III. The Sandstones of Morayshire, containing Reptihan re- 

 mains, shown to belong to the U])permost division of the Old Red 

 Sandstone." By Sir Roderick I. Murchison, F.R.S., D.C.L., 

 V.P.G.S.. &c. 



Referring to his previous memoir for an account of the triple 



