2 REPORT — 1880. 



address is, therefore, to attempt to sLow, that whatever may have been 

 the state of the world long before geological history began, as now written 

 in the rocks, all known formations are comparatively so recent in geologi- 

 cal time, that there is no reason to believe that they were produced under 

 physical circumstances differing either in kind or degree from those with 

 which we are now more or less familiar. 



It is unnecessary for my present purpose to enter into details con- 

 nected with the recurrence of marine foi'mations, since all geologists 

 know that the greater part of the stratified rocks were deposited in the 

 sea, as proved by the molluscs and other fossils which they contain, and 

 the order of their deposition and the occasional stratigraphical breaks in 

 succession are also famihar subjects. What I have partly to deal with 

 now, are exceptions to true marine stratified formations, and after some 

 other important questions have been considered, I shall proceed to discuss 

 the origin of various non-marine deposits from nearly the earliest 

 known time down to what by comparison may almost be termed the 

 present day. 



Meiamorphism, 



All, or nearly all, stratified formations have been in a sense meta- 

 morphosed, since, excepting certain limestones, the fact of loose incoherent 

 sediments having been by pressure and other agencies turned into solid 

 rocks constitutes a kind of metamorphism. This, however, is only a first 

 step toward the kind of metamorphism the frequent recu.rreuce of which 

 in geological time I have now to insist upon, and which implies that con- 

 solidated strata have undergone subsequent changes of a kind much more 

 remarkable. 



Common stratified rocks chiefly consist of marls, shales, slates, sand- 

 stones, conglomerates, and limestones, generally distinct and definite ; but 

 not infrequently a stratum, or strata, may partake of the characters in 

 varied proportions of two or more of the above-named species. It is 

 from such strata that metamorphic rocks have been produced, exclusive of 

 the metamorphism of igneous rocks, on which I will not enter. These 

 may be looked for in manuals of geology, and sometimes they may be 

 found in them. 



As a general rule, metamorphic rocks are apt to be much contorted, 

 not only on a large scale, but also that the individual layers of mica 

 quartz and felspar in gneiss are bent and folded in a great number of 

 minute convolutions, so small that they may be counted by the hundred 

 in a foot or two of rock. Such metamorphic rocks are often associated 

 with masses of granite both in bosses and in interstratified beds or layers, 

 and where the metamorphism becomes extreme it is often impossible to 

 draw a boundary line between the gneiss and the granite ; while, on the 

 other hand, it is often impossible to draw any true boundary between 

 gneiss (or other metamorphic rocks) and the ordinary strata that have 



