340 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



First ; from below, it differs little from Potsdam Sandstone. 



Secondly ; it consists of a fine yellow siliceous sand with carbonate 

 of lime, and fractures with a sparkling grain. 



Thirdly ; it is a yellowish calciferous material, intercalating with 

 a limestone like that of the Birdseye group. 



Near the middle, Calciferous Sandstone is cherty and geodiferous, 

 with Orthides. In its upper part it is occasionally oolitic in struc- 

 ture (Ballstone, &c). It frequently contains drops or buttons of 

 anthracite. 



Transition. — Calciferous Sandstone graduates slowly from Potsdam 

 Sandstone, and into either Chazy or Birdseye Limestones, in certain 

 localities. 



It rests directly on gneiss at Little Falls, &c, on the River Mo- 

 hawk ; but commonly its substratum is Potsdam Sandstone*. 



Place. — The northern and south-western outcrop or edge of Cal- 

 ciferous Sandstone follows closely the corresponding track of Pots- 

 dam Sandstone along the skirt of the elder metamorphic rocks of 

 the Laurentine Chain, for a distance of 1756 miles. It is equally 

 as extensive as Potsdam Sandstone, if not more so, sinking with 

 it under the more recent palaeozoic strata towards the centre of the 

 basin or area, but reappearing on the impulse of any intrusive rock, 

 as in Texas and elsewhere. 



Its direct eastern border from near Montreal runs with some 

 steadiness down the valleys of Lake Champlain and the River Hudson 

 for 550 miles alongside of Potsdam Sandstone, but, in the western 

 parts of the State of New Jersey, becoming both overlaid by younger 

 deposits, and involved in metamorphic influences ; it has not, as yet, 

 been seen further south in this vicinity. 



In the State of New York it is sometimes unexpectedly absent in 

 patches. 



Calciferous Sandstone is in general only seen in long strips, from 

 being covered up. In three places, however, if not in more, it over- 

 spreads surfaces several hundred miles long and fifty in breadth. 

 These places are, first, in the north-east of the State of New York, 

 a continuation of the Calciferous Sandstone of the Ottawa Valley ; 

 secondly, along the Upper Mississippi and "Wisconsin Rivers ; and 

 thirdly, on the River Osage, a large western affluent of the River 

 Mississippi. 



Position. — There is in general a slight dip toward the south and 

 west ; but in the north-west parts of the State it varies much and 

 suddenly, from the abundance there of intrusive rocks. In Jefferson 

 County it undergoes three or four uplifts vertically of 25-35 feet. 



In Franklin County the dip is to the N.W., and is slight ; in 

 Lawrence County it is to the N.N.E. ; and in Jefferson County the 

 dip is to the south. 



Thickness. — The thickness varies from 250 to 300 feet in the 

 N.W. of the State (Emmons) ; but, generally speaking, it is much 

 less in New York. 



* On the south-east side of Lake Superior, magnesia enters largely into the 

 composition of this early Silurian rock, according to Whitney and Foster. 



