24 TRANSACTIONS OF THE [ocr. 17, 
panied by microscopical and physical examinations, and more 
or less incomplete; so that we cannot obtain the exact know- 
ledge we need of the mineralogical constitution of the material. 
This objection equally applies to the two analyses, at the bottom 
of the table, of English dolomytes, celebrated for their durabil- 
ity. Chemical analysis alone may be entirely misleading in its 
bearing on the practical application of such stones to building 
purposes. 
Their strength and durability may depend partly upon the 
minerals of which they are constituted, 7. e., whether easily 
cleavable, soluble, or inclined to alteration, and partly upon the 
mode in which these constituent minerals are mutually arranged 
and cemented. The table shows that the majority of these 
marbles are nearly pure crystalline limestones, 7. ¢., consist 
chiefly of calcite ; the comparative softness and solubility of the 
grains, and the loose texture of their arrangement, account for 
the inability of nearly all of these marbles to endure either heavy 
pressure or long weathering. 
Others are dolomitic limestones, their grains are comparatively 
hard, strong, and insoluble; but their texture is so loose from 
the feeble mutual adherence of the grains, or their content of 
some soluble or oxidizable mineral, e. g., iron carbonate, is so 
great, that some of these stones also may be unfitted to resist 
either pressure, weather, or handling. Finally we have, in 
some of the famous crystalline dolomytes of England, materials 
fitted to resist all strain or attack, by their insolubility, closely 
compacted texture, and in some cases the filling up of all inter- 
stices by solid quartz. 
Near the northern end of the limestone belt now under con- 
sideration, in the fine quarry at Sutherland Falls, Vermont, an 
excellent opportunity is afforded to study the genetic history of 
this marble, perhaps the most compact and dense of any in that 
State, and the one exceptionally well fitted in that respect for 
out-door exposure as a building-stone. ‘Though remarkable for 
its general whiteness and fine grain, this marble is in part varie- 
gated with delicate bands of gray and bluish-gray color, which 
may be straight and parallel, more or less wavy, and even broken 
up into isolated patches of the grayish tints. On the face of 
the strata, at the back of the quarry, a few of these bands are 
more decidedly accentuated and continuous from top to bottom ; 
on one side inclining downward to the left (north), and on the 
other to the right (south). They thus obscurely mark the ori- 
ginal stratification and the position of the axis of a synclinal 
fold ; while their zigzag plications indicate the intense conden- 
sation and consolidation which the material has experienced 
during the process of folding. Of this action, the fine grain, 
