232 
life, then a solution of most important questions would be 
obtained ; as, for instance, the evacuation of sewage through 
a horizontal or level, or even an ascending course, to con- 
venient localities ; the supply of pure water to large towns ; 
the improvement of the common pump ; and if applicable to 
gaseous substances, the ventilation of mines as above sug- 
gested. 
ON THE OSCILLATION OF THE CURRENTS DRIFTING THE 
SANDSTONE BEDS OF THE SOUTH-EAST OF NORTHUM- 
BERLAND, AND ON THEIR GENERAL DIRECTION IN 
THE COAL FIELD IN THE NEIGHBOURHOOD OF EDIN- 
BURGH. BY H. C. SORBY, ESQ., F.G.S., SHEFFIELD. 
Those peculiarities of structure in sandstones, from which 
the direction and velocity of the currents which deposited 
them can be ascertained, have been so little attended to, and 
so imperfectly understood, that it will be desirable to explain 
their general nature, before entering upon their application 
to particular districts. 
If water, holding sandy particles in suspension, deposit 
them when tranquil, or when moving only very slowly over 
the bottom, the resulting beds are level and horizontal ; 
which structure I call " level bedded." If, however, the 
current move over the surface of the sand at the bottom with 
a certain moderate velocity, systems of waves are formed on 
it, trending, on an average, perpendicular to the line of the 
current, in the same manner as when a breeze blows over 
water. When, for a short interval, the velocity becomes less, 
these ripples become permanent, and thin layers may be 
deposited conformably over them, gradually becoming level. 
This process being repeated, a mass of rock may be formed, 
having a structure which I call " ripple laminated." By 
observing the direction of these ripple marks, the line in 
