244 



of drawing any distinct line of demarcation between the trachyte and 

 porphyry in those places where these rocks are contiguous, although 

 when at great distances from each other he allows the dissimilarity 

 of their respective characters. A stratified, pumiceous and trachytic 

 conglomerate, it is stated, frequently overlies the salt in Transylvania, 

 and contains impressions of dicotyledonous plants, leaves, and fishes. 

 The extinct craters of St. Annalake and the solfatarra still burning in 

 the trachyte of Budoskegy, and the many acidulated and mineral 

 springs, are considered by the author clearly lo indicate the recent age 

 of some of the volcanic phenomena in this country, to the principal en- 

 trance of which, the Romans assigned the name of "Vulcan's Pass." 



A paper was then read, " On the Astronomical Causes which 

 may influence Geological Phenomena; " by J. F.W. Herschel, Esq. 

 F.R.S. F.G.S., &c, &c. 



The author states his object in this paper to be, an inquiry into 

 the possible geological influence of slow periodical changes in the 

 orbits of the earth and moon, such as have been demonstrated by 

 geometers to take place in consequence of planetary and solar per- 

 turbation. Such influence he regards as extending only to the pro- 

 duction of changes in the amount of the tides and their consequent 

 erosive action on our continents, and of periodical fluctuations in 

 the quantity of solar heat received by the earth, every such fluc- 

 tuation being of course accompanied with a corresponding altera- 

 tion of climates ; and therefore, if sufficiently extensive and con- 

 tinued, giving room for a variation in the animal and vegetable 

 productions of the same region at different and widely remote 

 epochs. 



The subject of the tides is first considered. Since any approach 

 of the moon to the earth produces an increase of the lunar tide in 

 the triplicate ratio of such approach, it follows that any diminution 

 of the moon's mean distance must produce an increase in the ave- 

 rage tide during the whole period that such approach subsists. 

 The mean distance of the moon is actually on the decrease, and has 

 been so for ages past, producing the astronomical phenomenon 

 of her secular acceleration. The mean amount of the tides, there- 

 fore, has long been, and will long continue to be, on the increase 

 from this cause, but the effect of it is shown to be confined to such 

 moderate limits as to be of no geological importance. 



The author next considers the possible effect of an increase in 

 the excentricity of the lunar orbit, which would affect not the ave- 

 rage but the extreme rise and fall of the tides. Such an increase, 

 however, he regards as necessarily limited, so as to be incapable of 

 producing such an enormous increase of tides as would account for 

 any of the greater diluvial phaenomena, though possibly cases of 

 great local devastation in estuaries and confined channels would 

 arise, and the outlines of the continents, in particular parts of their 

 coasts, might be materially modified by such increased occasional 

 action. No change in the earth's orbit within the limits of possibility 

 would produce any material change in the solar tides. 



He next considers the effect of planetary perturbation on the 



