CALC1FER0US SANDSTONE. 119 



mechanically intermixed with fine grains of quartz and slight interlaminations of argilla- 

 ceous matter. In weathering, the Lime dissolves, and leaves in relief the silex ; and the 

 thin interlaminations, which often course along the surface in undulating lamina:, are of a 

 darker color than the hody of the rock. In consequence of the tendency to weather, it 

 presents a rough exterior when it has been long exposed ; still it is susceptible of form, 

 and as it splits into thick masses in consequence of being often thick-bedded, it becomes 

 an excellent material for construction, and has been largely used for locks on the canals. 



Another variety of this rock, is a fine-grained blue limestone nearly pure as a carbonate. 

 Its peculiarity consists in the possession of two prominent characters, a compactness with- 

 out lines of stratification, and an intermixture of white spar. Not unfrequcntly it appears 

 as if the whole had been broken up, and then reconsolidated by means of white calcareous 

 spar. The rock has not, however, been broken at all those places where these appear- 

 ances occur. It is probable the appearance has arisen from the rapid formation of the rock, 

 which, on drying, cracked by shrinkage, and into which cracks a pure calcareous matter 

 has infiltrated. This mass is beneath the former : in fact it is the lowest or oldest of the 

 deposites of this singular rock, resting directly upon the taconic or black slate. 



Another mass which comes under the Calciferous rock, is still farther removed from the 

 typical portion than the preceding. It is a red or chocolate-colored rock, consisting of 

 sandstone slightly interlaminated with shale : it is not much unlike lithologically to some 

 portions of the New Red sandstone. At Charlotte in Vermont, it is clearly a red sand- 

 stone ; and considered only as a local mass, it would pass for the Potsdam sandstone ; but 

 inasmuch as at some other points it is above the blue limestone of the preceding paragraph, 

 I have placed it in the Calciferous rock. Some portions are for a few feet a chocolate- 

 colored slate ; but in tracing it upwards, it is found to terminate in the gray calciferous 

 sandstone by imperceptible changes. 



This mass lies along the east shore of Lake Champlain. It does not appear in New- 

 York, unless we regard that curious brown rock of Mount Toby as an equivalent. The 

 vicinity of Burlington is the best region for forming an acquaintance with this mass. 



One variety still remains, which requires at least a passing notice. This occupies a 

 position above the last described : in fact, in tracing the chocolate sandstone upwards, we 

 find it losing its color, and while becoming lighter, it shows an increase of carbonate of 

 lime. It becomes, in the end, a fine-grained white limestone, sufficiently pure in many 

 places for quicklime. Generally it contains silex or sand, and preserves a reddish tinge. 

 In this condition it often resembles the Stockbridgc limestone ; though I have not observed 

 it in that saccharoidal condition, it is always much finer grained than the Stockbridge 

 limestone. But then again this variety passes into the ordinary calciferous sandstone, the 

 gray variety first described : hence its relations, and the place where it belongs, need not 

 be mistaken. 



I have noticed already four varieties of the Calciferous sandstone, and at no single 

 locality do they all appear. At St. Albans in Vermont, the blue, the brown and gray, 



