1861.] General Monthly Meeting, 345 



surface stream would cease, and would only recommence when the 

 flood rising to the brim of another natural dam, a new temporary 

 equilibrium would be established, a new horizontal superficial current 

 set in motion, and a second shelf or terrace begin to be eroded at the 

 higher level. So each of the parallel roads is conceived to have been 

 produced in the successive stages of the rising of one vast steady 

 incursion of the sea. The lapsing back of the waters, unaccompanied 

 by any sharp localized surface currents, through the passes, could 

 imprint no such defined marks on the surface, nor accomplish more 

 than a faint and partial obliteration of the terraces just previously 

 excavated during their incursion. This procedure was elucidated by 

 likening it to what takes place when we allow a steady but gradually 

 increasing jet of water to flow into a tank, perforated laterally with 

 several orifices at successive elevations, the outlets permitting a some- 

 what less rapid rate of discharge than is equivalent to the influx. If 

 such a tank be smeared internally with soft clay, the inpour can be so 

 regulated in respect to its acceleration, that the water, as it rises 

 successively to the levels of the several orifices will take on a hori- 

 zontal motion or current, through, first the lower hole, and then the 

 second and so on, and, remaining approximately stationary for a brief 

 while on the level of each, will groove the soft clay as it passes out, 

 until it swells above the orifice to reach the next. Some such process 

 as this at the notches which terminate the glens will, it is believed, 

 account for the terraces and all the features which belong to them. 



[H. D. R.] 



GENERAL MONTHLY MEETING, 

 Monday, April 1, 1861. 



William Pole, Esq. M.A. F.R.S. Treasurer and Vice-President. 



William Rutherford Ancrum, Esq. 

 Stephen Jennings Goodfellow, M.D. 

 William Newmarch, Esq. 



were elected Members of the Royal Institution. 



Rev. Alexander Denny, M.A. 

 Rev. Charles Forster, M.A. 

 Henri Gueneau De Mussy, M.D. 

 W. E. M. Tomlinson, Esq. 



were admitted Members of the Royal Institution. 



