No. 3.] AMERICAN ASSOCIATION. 103 



ON STAUROLITE CRYSTALS AND GREEN MOUNTAIN ONE18SE* 



OF SILURIAN AGE. 

 By Professor J. D. Daka. 



Prof. Dana has already published the fact alluded to by Per- 

 cival, that cryfitals of staurolite arc found in mica schist at 

 Salisbury, Conn., underlying directly the Stockbridgc limest-onc. 

 Since then he has found them in Southern Canaan, and at a 

 locality west of Housatonic River, but in this case the schifft 

 overlies the limestone. This staurolite also contains ganic*tj«. 

 The Stockbridge limestone is admitted to be Lower Silurian. 

 Prof Dana is sure that the Canaan limestone is identical witb 

 that of Stockbridgc. In any case there is no reason to doubt 

 that the staurolites occur in the later p;irt of the Lower Silurian 

 age, and strong reason for believing that these eehistfl ar« in aj;ye 

 veritable Hudson River rocks. On this view the Hudson River 

 or Cincinnati group in the Green Mountains — alike in Conneeti- 

 cut, Massachusetts, and Vermont — includes beds of quartait^^ 

 mica schist, cholritic mica slate, hydro-mica or talcos* slate, well 

 characterized gneiss and granitoid gneiss. 



The order of these deposits at South Canaan, Tyringham, and 

 <jrreat Harrington was then given, and the following conclasioii 

 reached : The fact that quartzite, limestone and gneiss, or mica 

 schist, here alternate with one another, is beyond question; and 

 if I am right in the age of the deposits as above suggested, the 

 alternations occur at the junction of the Trenton and Hudson 

 River formations. Other particulars respecting the geology of 

 the region referred to were given in Prof. Dana's paper, and the 

 conclusions reached that all old-looking Green Mountain gneissof* 

 are not pre-silurian ; and further, that the presence of staurolite 

 is no evidence of pre-silurian age. 



ON CIRCLES OF DEPOSITION IN SEDIMENTARY STRATA. 

 By Prof. J. S. Newberry of Columbia College, New York. 



The different strata which compose the geological column have 

 been divided into several groups, or systems, of which the base is 

 formed by the old crystalline rocks called Laurentian and Huron- 

 ian. On these rest the Lower Silurian System, composed of the 

 Potsdam sandstone, the Calciferous sandrock, the Trenton group 



