The Cambrian Rocks of North America. 77 



more or less exhausted stratum of comparatively insoluble and 

 ferriferous silicates, whence come melaphyres and basalts; partly 

 in the secondary or acidic zone, which, softened by the combined 

 agency of heat and water, may give rise to granitic and trachytic 

 rocks ; and partly, i t is conceived, in later aqueous deposits of 

 superficial origin, which may also be brought within the influence 

 of the central heat. 



This attempt to explain the genesis of crystalline rocks by the 

 continued solvent action of subterranean waters on a primitive 

 sti atum of igneous origin the author designates as the crenitic 

 hypothesis, from the Greek Kpnvt/ a fountain or spring. A prelimi- 

 nary statement of it was made by him to the National Academy of 

 Sciences at Washington, April 15, 1884, and appears in the 

 American Naturalist for June. 



III. The Cambrian Bocks of North America.* 

 By T. Sterry Hunt, LL.D., F.R.S. 



The writer gave his reasons for limiting the term Cambrian to 

 the Lower and Middle Cambrian of Sedgwick, which contain the 

 first fauna of Barrande. For the Upper Cambrian or Bala group, 

 holding the second fauna, wrongly claimed by some as a lower 

 member of the Silurian, and by others called Cambro-Silurian, 

 he prefers the term Ordovician, now accepted by many British 

 and continental geologists. This includes in New York the 

 Chazy, Trenton, Utica and Loraine divisions ; the Oneida 

 marking the base of the true Silurian or third fauna. The 

 Cambrian rocks of the great North-American basin may be 

 studied in four typical areas : 1. the Appalachian ; 2. the Adiron- 

 dack; 3. the Mississippi ; 4. the Cordillera area. To the first 

 of these belongs the immense volume of greatly disturbed 

 sediments along the whole eastern border of the basin, consti- 

 tuting the First Graywacke and the Sparry Limerock of Eaton ; 

 being the Upper Taconic of Emmons, and the Potsdam group and 

 Quebec group of Logan. They are distinct from the unconformably 



* Abstract of a communication to the Boston Soc. Nat. History 



Feb. 20, 1884. 



