442 Ss SJ. D. Dana—Taconic Rocks and Stratigraphy. 
occur very small in western Mt. Washington, and increase in 
abundance and size to the Housatonic; but are few and small 
in the arenaceous schist east of the Housatonic. 
e. Staurolites occur of very small size in the southern half 
of eastern Mt. Washington, and are, on an average, twice 
longer in eastern Salisbury. In the northern half of Mt. 
Washington, staurolites have not been found, but they occur 
in the coarsish mica schist three miles farther east. (This in- 
terval of three miles is occupied by limestone so that no nearer 
observation is possible. 
. Orthoclase is very sparingly present in the hydromica 
(or sericite) schist to the west; but is less rare in the mica 
schist west of the Housatonic, and still less so in part of the 
uartzytic mica schist east of the Housatonic; in some of it, 
the feldspar is partly the species microcline. 
Looking at the constitution of the minerals, we learn that to 
the west of the area of Mt. Washington the sediments of 
which the rock is made were very fine earthy, containing little 
quartz; that the amount of quartz sand in the sediments 1n- 
creased to the eastward; and that toward the eastern limit of 
the region, sand was the chief material. The occurrence 0 
arenaceous mica schist overlying, underlying and interlaminat- 
ing quartzyte beds indicates a small change at intervals in the 
kinds of depositions such as may have come from changing 
depths or currents. . 
All the facts derived from the constitution of the rocks point 
to a single system of hydrographic conditions and sedimenta- 
tion ; and none suggest the subsequent occurrence of great dis- 
placements by long overthrusts any more than those that have 
een gathered from the stratigraphy. The lithological obser- 
vations accord with the stratigraphical. 
The stratification described is true stratification and not that 
of a subsequently induced cleavage-structure ; for the beds of 
mica schist, quartzyte and limestone are parallel in interlamina- 
tions and interstratifications. Cleavage structure is a common 
source of lamination in the hydromica (sericite) slates west of 
Mt. Washington ; and hence the true planes of bedding ca? 
there be learned only from the contact portions of the lime- 
stone and slates; but it is much less common farther east; a2 
the danger of error has been avoided in the observations I have 
made by taking them at or near the contacts of the different 
strata or rocks. 
