222 Intelligence and Miscellaneous Articles. 



occur as a lenticular mass, 21 ft. thick at its maximum, in a hollow of 

 loose yellow sand ; the current-bedding of the upper loamy layers is 

 very marked towards the north end, with, a strong false dip to the 

 south, i. e. towards the centre of the basin. 



Accepting as the true datum line for the base of the Middle 

 Bagshots in this district, "the foliated clays, more or less sandy, 

 having a thickness of 14 ft.," which are shown by Prof. Prestwich 

 to be typically developed in the railway-cutting on Goldsworth Hill, 

 it was contended that the Hatch brick-earth cannot be correlated with 

 these. The true basal beds of the Middle Bagshots in this district 

 differ somewhat in their physical characters ; but it was on strati- 

 graphical grounds mainly that the Author endeavoured to show 

 that the Hatch brick-earth should, despite its argillaceous nature, 

 be assigned to the Lower Bagshots. A diagrammatic section from 

 St. George's Hill (245 ft.), through "Woburn Hill (92 ft.), to St. 

 Ann's Hill (230 ft.), was given, and the possible existence of a trough 

 or synclinal towards the centre of the section discussed. It was shown 

 from the position of the Hatch brick-earth that if the Lower Bag- 

 shots retain anything like the mean thickness of, say 120 ft., which 

 prevails in this district, the London Clay surface must here be 60 ft. 

 below 0. D., on the supposition that these beds represent the basal 

 clays of the Middle Bagshots ; whereas, at Chertsey, in the valley 

 of the Thames itself, the London Clay surface coincides with 0. D. 



In conclusion, it was held (1) that the more we study the Bagshot 

 beds of this area the less likely are we to see a passage between the 

 curiously diversified Lower Bagshots and the much more uniform 

 and homogeneous London Clay ; (2) that, until we realize the con- 

 siderable though sporadic development of clays in the Lower Bag- 

 shots, we shall be in danger of referring beds to the Middle Bag- 

 shots which do not belong to them, and thereby give encouragement 

 to a speculative stratigraphy which can only mislead. 



XXYI. Intelligence and Miscellaneous Articles. 



A NEW METHOD OF REDUCING OBSERVATIONS RELATING TO 

 SEVERAL QUANTITIES. 



To the Editors of the Philosophical Magazine and Journal. 



GrENTLEMEN, 



IX/FAY I call the attention of your readers to a method of redu- 

 -*-"-*- cing observations relating to several quantities, which I have 

 described in the current number of Hermathena (Trinity College, 

 Dublin). This method is a generalization of that Method of Situa- 

 tion which Laplace has applied to observations relating to a single 

 quantity, in the second supplement to his Theorie Analytique. 



The method may be thus described in the case of two variables, 

 x and y. Find an approximate solution by some rough process 

 (such as simply adding together several of the equations so as to 

 form two independent simultaneous equations). Take the point 



