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continent. To none am I more indebted than to my friends Pro- 

 fessors Judd and Lapworth in England, to various workers in 

 Canada and in the United States, and to Heim, Lehmann, and the 

 members of the Geological Survey of Switzerland, whose maps have 

 been of late years of the greatest help to me. Still I have studied 

 nature in regard to these subjects more than I have studied books ; 

 because, owing to the difficulty of being quite certain of the sense 

 in which the author was using his words, and the scepticism produced 

 by finding upon how slight a basis of fact important generalizations 

 had been made to rest, I determined at the outset to test every- 

 thing for myself, and take as little as possible on authority or for 

 granted. If then there is any value in my results, it will be that 

 they have been obtained, as far as possible, independently, and 

 sometimes actually in iguorance of the work of others ; e. g. 1 had 

 arrived at conclusions which in certain respects agreed with those of 

 Heim and Lehmann before I had read their books. 



My task to-day will be rendered more easy by a few preliminary 

 remarks on the structures of which I have to speak, and a brief 

 outline, in anticipation, of the conclusions to which I have been led. 

 • Eoliation may be produced, as has not seldom been pointed out, 

 by the action of pressure during crystallization. Thus it may occur 

 in an igneous rock, as a structure produced while the mass is 

 cooling. Of this, however, I do not at present speak ; such a structure 

 is often local, and is always abnormal ; that is to say, it is a de- 

 parture from the ordinary mode of crystallization of an igneous rock, 

 in which there should be no definite orientation of the constituent 

 minerals. In these cases, however, the minerals retain substantially 

 the characteristics which they exhibit in the normal rock, into 

 which frequently they pass by almost insensible gradations ; indeed, 

 not seldom, the "foliated" structure is more conspicuous macro- 

 scopically than microscopically. The great mass, however, of the 

 rocks ordinarily designated "foliated," the normal gneisses and 

 schists, exhibit structures which are not less, perhaps more, con- 

 spicuous when seen under the microscope than they are in the field, 

 and to these rocks a sedimentary origin of some kind has been 

 generally assigned. Putting by for the present the question of their 

 genesis, I wish at this stage to distinguish clearly between two 

 kinds of foliation which I have observed, in order that, for the sake 

 of brevity and perspicuity, I may use distinctive terms in my future 

 remarks. In many cases we find rocks of very difierent mineral 

 character, for example, quartzites and mica-schists, alternating one 

 with another so as to make it in the highest degree probable that 

 they are stratified rocks — indeed, it seems in many cases almost 

 certain that they were once beds of sand, silt, mud, &c., which have 

 subsequently undergone mineral rearrangement. Now in many of 

 these we find that there is a very definite orientation of certain of 

 the mineral constituents ; the mica-flakes, for example, in one of these 

 micaceous schists, lie roughly parallel one with another, and with 

 the apparent bedding-planes of the masses. Further, in a number 

 of other rocks of more uncertain origin, as, for example, some of the 



