176 Proceedings of the Royal Physical Society, 
mesozoic and tertiary series of strata, where pervious strata, 
capped by those which were impervious, have an area of 
many miles in extent. The lower greensand, for instance, 
which surrounds the London basin, is capable of absorbing 
daily the enormous quantity of 146,000,000 gallons of water, 
and this bed alone has a subterranean area estimated at 4600 
square miles. Mr Prestwick assumes the thickness of this 
bed to be 200 feet, so that the whole capacity of the subter- 
ranean water-bearing mass will be equal to 920,000 square 
miles, one foot thick. The hydraulic forces resulting from 
the pressure of the overcapping strata on this bed, which is 
virtually a water reservoir, will act in two directions, and 
the pressure will be equal. A force will unitedly press from 
either side of the basin ; and the most powerful strain of 
both will be on the centre of the basin. It is certainly, 
then, somewhat curious that a fault generally should be 
found in the centre of these Jurassic and tertiary basins ; 
and that the course of a river should generally be in the line 
of this fault. Add to this the fact, that borings for artesian 
wells are generally successful only within twenty metres of 
the river, and there appear to be sufficient data to excite 
the inquiry whether such hydraulic pressure, as no doubt 
actually exists in the strata, may not have been the proxi- 
mate cause of these faults. 
III. Ornithological Notes. ( With exhibition of Specimens.) 1. Anthro- 
poides virgo (Numidian Crane) ; 2. Syrrhaptes paradoxus (Pallas' 
Sand- Grouse) ; 3. Falco subbuteo (Hobby) ; 4r. Pernis apivorus 
(Honey Buzzard) ; 5. Bomby cilia garrula (Bohemian Waxwing) ; 6. 
Botaurus stellaris (Common Bittern) ; 7. Botaurus lentiginosus 
(American Bittern) ; 8. Mergulus melanoleucos (Rotche or Little 
Auk); 9. Circus cyaneus (Hen Harrier); 10. Parus cristatus 
(Crested Titmouse) ; 11. Loxia curvirostra (Common Crossbill) ; 
12. Alauda arvensis (Sky-Lark — a black variety) ; 13. Phalaropus 
lobatus (Grey Phalarope). By John Alex. Smith, M.D. 
Since the close of last session some of our rarer birds 
have been captured in different parts of the country. I shall 
refer to several which have come under my own immediate 
notice, taking them principally in the order of their oc- 
currence : — 
