METAMORPHISM. 755 



sil crinoids, corals, and shells along part of the West Rutland Val- 

 ley, along a portion of the belt between two ranges of marble quarries, 

 aud at other points in Vermont, and also to the south, in Dutchess 

 Co., New York. Similar evidence has been observed at Lake Mem- 

 phremagog, at Bernardston, Mass., in the Sierra Nevada, in Cornwall, 

 in France, Norway, the Urals, the Tyrol, the Alps, and in many other 

 regions. At Brevig, Norway, a Silurian limestone with fossils con- 

 tains also garnets and scapolite ; in the Urals, Murchison found a 

 crystalline limestone containing encrinites ; schists in Brittany are 

 described by Boblaye as affording andalusite crystals and species of 

 Orthis, Spirifer, and Calymene, in one and the same specimen ; at 

 Rothau, in the Vosges, in a hornblende rock, corals have been replaced, 

 as stated by Daubree, without losing their form, by crystals of horn- 

 blende, garnet, and axinite ; among the corals the species Calamopora 

 spongites is quite distinct. In view of such facts, the fact of regional 

 metamorphism is no longer a mooted question. 



2. Effects of Metamorphism. 



The principal effects of Metamorphism upon rocks are the follow- 

 ing: (1) Consolidation; (2) Loss of water or other vaporizable in- 

 gredients ; (3) Loss of material by chemical solvents ; (4) Change of 

 color ; (5) Obliteration of fossils ; (6) Crystallization without a change 

 in the combinations present; (7) Crystallization with more or less 

 change in the constituent minerals of the rock. 



i. Consolidation. — Ordinary atmospheric or subterranean waters, 

 however prolonged their action, do not necessarily produce solidifica- 

 tion. The soft sandstones of all ages, from the Potsdam to the inco- 

 herent beds of the Quaternary, are evidence on this point. It is 

 probable that deposits have existed to an immense extent in past time, 

 that failed to be consolidated, and consequently were washed away in 

 the course of subsequent changes. 



But while there are many fragile Potsdam sandstones, there are 

 others, as those of eastern New York and Vermont, that have been 

 hardened, through some process, into quartzytes and quartzose gneisses, 

 and deposits of sand and pebbles of various other ages that are re- 

 fractory sandstones and grits. That the consolidation is due to cir- 

 cumstances of a metamorphic nature is often evident from their posi- 

 tion within, or on the outskirts of, regions of other metamorphic rocks. 

 In the same way, fragile absorbent argillaceous shales have been har- 

 dened into firm non-absorbent slates. 



At the Geyser region of Yellowstone Park, according to F. H. Bradley, the sand-beds 

 of a terrace on Shoshone Lake, over a hundred feet high, have been firmly consolidated, 

 to as to look like quartzyte; and this was done by the hot siliceous waters, when the 

 waters of the lake stood at a higher level. 



