28 



many undoubtedly igneous rocks have a more or less well defined 

 banded structure and parallel arrangement of the constituents, induced 

 by the movement of the rock while in a liquid or viscous state. Some 

 such motion it was thought might produce the foliated structure seen 

 in these gneisses and allied rocks . Of course since the earth is supposed 

 to have solidified first at the surface, the higher meoibers of the series 

 must be older than those on which they rest. This hypothesis found 

 many illustrious supporters, but does not by any means satisfactorily 

 explain the repeated alterations of difierent varieties of gneiss, lime- 

 stone quartzite and other rocks, seen in the Laurentian system. 



Dana, in 1843, * put forward a modification of this hypothesis. He 

 supposed that gneiss and mica schist bore to granite a relation some- 

 what similar to that which volcanic tuS" and debris bears to our modern 

 lavas. He saw in these rocks the products of great volcanic eruptions 

 which took place imder great pressure at the bottom of the ocean and 

 which were compacted and altered by the action of the superincumbent 

 waters highly heated by the eruption. The enormous extent and thick- 

 ness of the primitive formations and their occurrence, frequently quite 

 independent of larger granitic masses, do not favour this view. Dana 

 himself subsequently saw reasons for rejecting it, and says of the 

 Laurentian rocks in his Manual of Geology published in 1875 : — " The 

 alternations of hornblendic and other schists, with quartzite, limestone, 

 gneiss and other I'ocks, prove that all were once sedimentaiy beds, beds 

 formed by the action of moving water, like the sandstones, argillaceous 

 beds, and limestones of later times. They have no resemblance to lavas 

 or igneous injections." And again " these Laurentian rocks are made 

 out of the niins of older Laurentian, or of still older Archcean rocks, 

 that is, of the sands, clays and stones made and distributed by the 

 ocean, as it washed the earliest formed crust of the globe." The 

 second hypothesis has been ably advocated by Dr. Sterry Hunt. It 

 agrees in some respects, though differing in others, with the old 

 neptunian theory of Werner. Werner taught that all rocks, eruptive, 

 crystalline and sedimentary, were deposits from the waters of a pi'imeval 

 ocean. According to this theory all silicated, stratified rocks, and pro- 



* American Journal of Science — 1843, p. 105. 



