296 APPENDIX 



difficult field, more especiall)' by Dr. Ells, Dr. 

 Adams, and Mr. Barlow, which it may be hoped 

 will go far to settle finally the arrangement and 

 distribution of pre-Cambrian rocks in the Northern 

 part of the American Continent. The maps and 

 detailed reports representing these explorations are 

 not yet before the public, but from some preliminary 

 notices which have appeared in scientific periodicals, 

 it may be inferred that the distinction between the 

 fundamental gneiss, with its associated igneous pro- 

 ducts, and the Upper Laurentian, will become 

 greater than was supposed by Logan. The Lowest 

 Laurentian or Trembling Mountain series of Logan 

 now represents a very widely extended basement 

 formation, not so far as can be ascertained, com- 

 posed of sedimentary rocks in a metamorphosed 

 state, but rather of peculiar aqueo-igneous materials, 

 different from the greater part of those which 

 succeeded them, and associated with varied and 

 extensive igneous intrusions and in-ineltings like 

 those which Keilhau ascertained long ago in the 

 case of similar rocks in Norway. The Grenville 

 series, on the other hand, may prove to be a 

 remnant of an overlying system, originally less 

 extensive or bordering the older group, and greatly 



