﻿ANNIVERSARY ADDRESS OP THE PRESIDENT. llX 



Member of this Society in 1827) described a dyke of great extent, com- 

 posed of saccbaroid limestone, traversing a granitic ridge in the 

 Bergstrasse, between tbe villages of Auerbach and Schonberg ; it was 

 specially noticed by Von Leonhard* in 1833, who says of it, tbat 

 a close examination left tbe impression tbat it was erupted in a state 

 of igneous fluidity from tbe depths of tbe earth subsequent to the 

 formation of the gneiss ; for the granitic rock there appears both with 

 a gneissic structure and as syenite. And in 1852 Voltzf thus de- 

 scribes it : — " The whole appearance of the limestone is that of a 

 dyke ; and there can be no doubt that we have one of colossal size, — 

 the limestone being crystalline, and showing all varieties of structure 

 from fine-grained to calcareous spar." Similar occurrences have been 

 described by Emmons in the State of New York, by Clarke in Au- 

 stralia, and by Dumas in tbe CevennesJ ; and instances of veins of 

 large dimensions of calcareous spar, with numerous ramifications, 

 having as much the appearance of injection from below as veins of 

 granite or trap, must be familiar to every geologist. 



The gneiss of Norway and Sweden, in many parts, contains, dis- 

 seminated through the substance of the rock and in masses of vast 

 magnitude, ores of magnetic iron, of silver, copper, cobalt, zinc, and 

 arsenic ; in Saxony it has been found containing tin, arsenic, iron, 

 and copper ; in France, in the department of the Aveyron, it abounds 

 in magnetic iron ; and the same combination is met with in different 

 parts of the United States. These metallic minerals are surely 

 much more probably of subterranean than of sedimentary origin. 



There is no manner of doubt that there are vast tracts of gneiss 

 with such distinct stratification, often greatly contorted, to which no 

 other than a sedimentary origin can with any degree of probability 

 be ascribed, however difficult it may be, in the present state of our 

 knowledge, to comprehend the nature of the chemical action by which 

 the original component materials have been altered into new com- 

 binations. On the other hand, the assertion that all gneiss has 

 had the same origin appears to me erroneous, for the reasons I have 

 assigned ; and it is distinctly contrary to the opinion of some of the 

 most distinguished geologists of Prance and Germany. 



A rock is now very commonly said to be metamorphic in such a 

 variety of cases, without any qualification of the term, whether in 

 relation to the nature of the materials acted upon, or to the totally 

 different texture of the rocks beneath, which have for hundreds or 

 thousands of feet undergone no similar alteration, that it is im- 

 possible to arrive at any other conclusion than that there must have 

 been different agencies at work — that the subterranean thermal 

 action considered to have produced gneiss from detrital matter could 

 not have produced the crystalline rock intercalated in a tertiary de- 

 posit. PalaBontological determinations are made under the guidance 

 and control of the acknowledged laws of anatomy and physiology ; 



* Neues Jahrbuch fur Mineralogie, &c, 1833, p. 312. 



•f Uebersicht der geologischen Verhaltnissen des Grrossherzogthum Hessen, 

 p. 107. 



\ Naumann, Lehrbuch der Greognosie, 2nd edition, vol. ii. p. 88. 



