lxXX PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [March I913, 



persons who feel strongly the desirability of records being preserved, 

 and make a point of informing us when boring operations are 

 undertaken ; but it happens too frequently that we hear of a bore- 

 hole having been made, too late for au adequate examination of 

 the cores. Others we never hear of, nor are the cores submitted 

 to any competent geologist; and in such cases records, if preserved 

 at all, are apt to be worse than useless. Any hard rock is liable 

 to be called granite ; Lower Palaeozoic shales, if they are black, 

 become Coal Measures ; all red rocks are ISTew Bed Sandstone. 

 This is not the time for suggesting the exact form of the machinery 

 whieh should be created for the preservation of boring records, but 

 I take the opportunity of expressing to you my opinion that our 

 methods of exploration are at present happy-go-lucky and unworthy 

 of our great mineral heritage. 



There are, however, other lines of investigation to which I wish 

 to direct attention as offering a prospect of throwing more light upon 

 the nature of the complicated mass of Palaeozoic rocks which lies 

 under our feet. As geologists, we learn with pleasure from the last 

 Beport of Progress of the Ordnance Survey that a revised levelling 

 of the British Isles is in progress. 



In the primary levelling, which was carried out in the years 

 1841 to 1859, the precision is not of a modern standard. The 

 levels, moreover, were recorded by rough marks on various objects 

 which were often not permanent. The new levelling has been 

 planned with the object of determining relative altitudes with the 

 utmost attainable precision, and of recording levels by permanent 

 marks which are founded on rock below the subsoil, and are, so far 

 as can be foreseen, free from suspicion of shifting from any cause- 

 whatever apart from movement of the earth's crust. Various 

 difficulties, to which I need not now refer, arose in the selection of 

 suitable sites for these ' fundamental points'; but in the levelling, 

 when carried out with such precision as is contemplated, certain 

 factors of unknown value may have to be taken into account. 

 Among these I may mention the existence of earth-tides, and also 

 the effect of the oceanic tide in temporarily depressing the coast 

 upon which it impinges. 



Put what I have in my mind more especially is the variation 

 in gravity which is known to exist, but has never been syste- 

 matically investigated in the British Isles. A large number of ob- 

 servations on the deflection of the plumb-line and on the varying 



