Report on the Geological Survey of Connecticut. | 171 
in quarrying this rock ; but from such facts as could be 
is believed that they ordinarily fall but little below five sete 
The properties of the gneiss are in a measure peculiar: at least, no 
rock precisely resembles it in any part of the State. Its leading 
peculiarities depend upon its black mica and transparent grains of 
albite. ‘These are arranged in thin, strait, and parallel layers, giving 
to surfaces produced by cross-fracture a banded appearance of black 
and gray; while the surfaces resulting from cleavage are almost 
black. Both the mica and the albite possess high degrees of lustre, 
which impart to the rock a very brilliant effect,—rendering fresh 
slabs of it almost insupportable to the eyes, in a strong light of the 
sun, The-cleavages do not take place with the greatest freedom, 
and can rarely be effected, so as to divide the rock into slabs of less 
than six inches in thickness.* They are particularly prone to occur 
where the mica is most abundant, and this in general is contiguous 
to those layers of albite which are made up of larger individuals 
than the average size. The rock contains very little quartz. Horn- 
‘blende is occasionally present, which is of a black color, highly 
crystalline, and brilliant in its lustre. The process of quarrying 
appears to be conducted with the greater facility, from the highly 
inclined position of the strata. Slabs of any dimensions are easily 
procured. Its great use seems to be for flag and curb-stones, though 
it is also employed extensively in the construction of wharves, 
bridges, breakwaters and fortifications, for which purposes its strength 
and inalterability render it very desirable. It is likewise used for 
underpinning stones, and for posts to gateways and fences which in 
some instances are covered by wood. As it is a material of great’ 
importance in paving, it is sought for in all the large cities, being 
extensively used in Boston, New York and Philadelphia, and of late 
has been introduced into Charleston and New Orleans, where it is 
recently 
likely to prove highly important in the paving improvements 
commenced in these cities. It may well be doubted whether any 
"material will be brought to light in the country, better adapted either 
in quality or local situation than the gneiss of the Connecticut river, 
for satisfying these demands. 
‘‘In the northwestern part of Lebanon, a little east of what is 
called Hearth-stone hill, a very valuable flagging is quarried. It 
consists of a feldspathic gneiss. It is very thinly stratified, strait 
* Many of the flagging stones sold in New Haven are not more than one, bw, or 
three inches thick, and come, we believe, from Haddam.—Ep. 
