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KENDALL : PRESIDENTIAL ADDRESS. 
and the}^ have been discussed by Marr and myself on several 
occasions, but the conclusions reached will probably need much 
revision. 
Out of Sorby's researches into the microscopic structure of 
minerals and rocks has grown the great and progressive science 
of Petrology, a branch of Geology that has developed methods 
of extraordinary refinement and precision. A pebble a quarter 
of an inch in diameter may now be sliced and submitted to an 
optical analysis that will not only disclose its mineral constituents 
and structure, but will reveal its mode and place of origin and the 
vicissitudes through which it has passed. The subject is too 
gigantic to be more than hinted at here, but it may be observed 
that the study of this branch of Geology supplies just that element 
of exactitude and precise measurement, the assumed absence of 
which has often been made matter of reproach by the cultivators 
of the physical sciences. 
It may suffice to say that the Petrological study of the rocks 
of Yorkshire has been prosecuted with success by Sorby himseK, 
as well as by many of his successors. 
There is one topic which, dangerous as it is, I can hardly ; 
venture to ignore since members of this Society have had a large 
share in its discussion. This is the important matter of Glacial 
Geology. 
In the earl}^ part of the Nineteenth Century, the opinion was 
universally held by geologists that the tumultuous accumulations 
of rock-debris that we call collectivel}^ Drift, were the products 
of the Noachian Deluge, and hence these deposits were called, and 
still are so designated on the Continent, Diluvium. Having 
settled this point, the chief business of the early geologists was to 
discover the mechanical agencies by which this catastrophe was 
brought about. 
Murchison and other geologists of the mid- Victorian age 
invoked great " waves of translation " sweeping out from the 
mountains and hurling boulders and all the rest of the Diluvial 
materials before them like dust before the broom. 
Whewell was for a similar heroic treatment, and would heave 
up mountain massifs, such as the Scandinavian chain, \\'ith a few 
vigorous strokes, and in the best manner of his kind, having 
