216 Mr. Sowerhy on the Geology [S ept. 



Others may be left out. In this case, the specific gravity being 

 taken at -534, will not give the result exactly as above. Hence 

 the above formula becomes a means of finding the exact specific 

 gravity, which will be -5347. I am, yours truly, 



C. Sylvester. 



Article IX. 



On the Geological Formations of Headen Hill, in the Isle of 

 Wight. By G. B. Sowerby, FLS. 



(To the Editor of the Annals of Philosophy.) 



SIR, 

 The combined efforts and abilities of a most respectable and 

 learned Society have been exerted for some years in the cause of 

 geological science ; their attention has been directed to the care- 

 ful examination of various interesting districts ; facts of vast 

 importance have been ascertained, and the volumes of then- 

 Transactions are stored with considerable and useful information 

 upon the various points in connexion with, and generally leading 

 to the discovery of, truth in their pursuit. Notwithstanding, 

 however, the zeal by which their exertions have been stimulated, 

 and the great degree of labour with which they have been accom- 

 panied, it will, I think, appear to any reflecting mind, that their 

 success, and the consequent increase of geological knowledge, is 

 not proportionably great. We are but just arrived at that stage 

 in which we begin to discover the existence, and to estimate the 

 extent, of our ignorance — ignorance rather the result of wilful 

 negligence than of unavoidable necessity. In support of this 

 opinion, I will appeal to that reply which must be given to the 

 following plain question : How can any person know the nature 

 of any stratum, until he have taken the pains to make himself 

 acquainted with its constituent parts ? For instance, can any 

 person decide upon the nature of amass of granite until he know 

 how to distinguish among minerals the three substances of 

 which it is composed ? How can any person decide confidently 

 on the nature of a shelly stratum, unless he know whether the 

 shells which characterize it be land, or freshwater, or marine'? 

 The undisputed importance of geological investigation renders it 

 extremely desirable to collect the most undoubted evidence of 

 facts as they are, before we can hope to arrive at any thing like 

 certainty in the conclusions we may be disposed to draw from 

 them. Every particle of information that can be gained is, 

 therefore, of some consequence. These are my reasons for 

 troubling you with the following observations collected during a 



