117 



.LIBR, 



ELEMENTARY LECTURE ON GEOLOGY. V*^" 



BY R. W. ELLS, LL.D., F.G.S.A. \ *^ m. 



Delivered on Monday Afternoon, January 21, 1889. 

 In attempting to prepare a paper for this Society on the subject of 

 Geology, I must confess [ have found myself at a considerable loss to 

 know how best to discuss it for such is its greatness and so limited 

 the time at my disposal that the utmost economy of material must be 

 exercised in order to touch even upon the leading points. I have 

 thought however that possibly a brief sketch of the views held from time 

 time as to the origin and early history of our eartli might be of interest 

 first of all, and then we miglit present a brief outline of the several 

 systems into which the science is generally divided. 



Strictly speaking, Geology is the science which tells us about the 

 earth. It investigates the many changes which have taken place on 

 its surface, both in relation to organic and inorganic matter as well as 

 the causes which have produced these changes and the influence which 

 they have exercised. It may for the sake of convenience be considered 

 under three heads, structural, dynamical and historical, though some 

 authors make a much more elaborate division of the subject. Of these the 

 first. Structural geology, deals with the general form and structure of the 

 earth, the kinds of rock, whether sedimentary or stratified or igneous and 

 unstratihed with their mode of occurrence, eithev 2)lutonic or deepseated, 

 not reaching the surface, or eruptive, volcanic and reaching the surface. 

 It takes cognizance also of the metamorphic rocks and the manner in 

 which the metamorphism has been effected, as well as the general condi- 

 tion of the eai-th's crust, as affected by faults, joints, veins, etc. It also 

 considei's the origin and structure of mountains and many similar sub- 

 jects connected with the earth's architecture. 



The second. Dynamical geology, treats of the forces or agencies by 

 which the several changes have been effected, whether aqueous, igneous 

 or organic. Among the first of these, the aqueous, may be classed 

 rivers, seas, glaciers, &c. The 2nd, or igneous, refers to the agency of 

 the internal heat of the earth, as volcanoes and their resulting efi"ects, 

 geysers, etc. ; whilst the 3rd, or organic, includes, 1st, vegetable accu- 



