261 



accompanied the great breach in it towards the sea; and a third, 

 which probably produced some local streams, such as that of Marino, 

 which has evidently flowed since the ground took its present con- 

 figuration, and was covered with plants. Of lavas, likewise, we must 

 admit at least three periods ; 1st, the compact basalts of the outer 

 circuit, which, if Von Buch's theory bo correct, have flowed under a 

 less inclination than they at present have ; 2dly, The well-marked 

 leucitic, or partridge-eyed lavas, which form the interior circuit ; 

 and, 3dly, the compact basaltic lava which flows past Rocca di Papa 

 towards Grotta Ferrata, which is possibly coeval with the dikes oc- 

 curring at Capo di Bovo and elsewhere. This leaves the origin of 

 the lava sperone still uncertain. It is undoubtedly one of the more 

 recent products, for it not only overlies the whole of the old basaltic 

 series at Tusculum and Nemi, but the leucitic lavas of the newer cone 

 at Rocca di Papa. The easiest solution would be to consider it as a 

 scoriform basalt ; but even to this there are difficulties, not only mine- 

 ralogical, but from position. For how can we connect the mantle- 

 shaped covering of Monte Cavo up to its highest point, with the basalt, 

 which nowhere attains a height (so far as I know) within several 

 hundred feet of it ? It is still more difficult to conceive any contin- 

 uity between the sperone of the central cone and that of Tusculum, 

 which is separated from it by the great valley of La Molara. 



The following gentleman was duly elected an Ordinary 

 Fellow : — 



W. J. M. Eankine, Esq., C.E. 

 The following Donations to the Library were announced : — 



The Phenomena Diosemeia of Aratus, translated into English verse, 

 with Notes. By John Lamb, D.D. 8vo. — By the Author. 



Abstract of Exposition on the Strength of Materials. Read before 

 the Royal Scottish Society of Arts at the request of the Coun- 

 cil. By George Buchanan, F.R.S.E. 8vo. — By the Author. 



Sopra alcuni puuti della Tcoria del Moto dei Liquidi. Memoria del 

 Prof. P. Tardy. 4to. — By the Author. 



Annalen der K. Sternwarte bei Miinchen, herausg. von Dr J. La- 

 ment. Bde. 1 & 2. 8vo. — By the Observatory . 



