186 
THE NATURALISTS’ COMPANION. 
Sandstone Houses. 
BY G. H. SELOVEK, LAKE CITY, MIKN. 
A few days ago I happened to notice, 
on my way to St. Paul, a number of 
small holes in the sandstone cliffs, a 
mile or so east of the city. On return¬ 
ing, I thought I would investigate 
somewhat, and found that they were 
not produced by any natural cause, but 
artilicially, as it were, by the various 
kinds of sw^allow's. Very few' of these 
“cliff houses” w'ere in reach, as these 
cliffs are from sixty to eight}' feet high, 
and the holes were all within twenty 
feet of the top. Those in reach froni 
the top proved to contain young of the 
Cliff, Bank, and Rough-winged Sw'al- 
lows. Very few% on account of the ad¬ 
vanced time of year, contained eggs, 
and these were all nearly hatched. 
The holes were made in the stone by 
the birds as nesting places, and were 
between ten and thirty inches in depth 
by from one and a half to three inches 
in diameter. 
Will some one wdio is more conver¬ 
sant with the habits of these species 
than myself, please let me know' wdieth- 
er this is a usual occurance? As for 
myself, I have often seen Bank 
and Rough-winged Sw'allow's burrow¬ 
ing in to the soft clay banks but never 
before into hard sandstone. 
Limestone. 
Read at the first annual meeting of Choapter 7fi(t of the 
Agassiz Association, Jamaica Plain, Mass. 
There is scarcely a family of miner¬ 
als, excepting the (piartz, that furnish¬ 
es so many specimens to the collector 
or mineralogist as limestone. What 
collection would be complete without 
specimens of Iceland spar, satin spaiv 
calcareous tufa, and stalactites, which 
when polished are often more beauti¬ 
ful than agates. If all the fossils com¬ 
posed of calcite w'ere to be annihilated, 
the geologist would lose many of his 
most interesting specimens. He would 
lose almost every fossil shell and shell¬ 
fish and many fossil plants and leaves. 
Limestone is of great interest to others 
besides those w'ho look upon minerals 
as something to be collected in vacation 
to be placed in cabinets, or those who 
look upon them from a scientific point 
of A'iew. For the fine arts it is used 
almost universally, being employed in 
almost every case for sculpturing and 
ornamental w'ork. It is of great value 
as a building stone, some varieties even 
surpassing granite for durability. 
This important family comprises 
one-seventh of the earth’s crust. It 
includes all minerals that are compos¬ 
ed of calcite or carbonate of lime: that 
is, carbonic acid united wdth lime. 
Among the most important varieties 
of this family are many kinds of mar¬ 
ble, Iceland spar, satin spar, chalk, 
stalactites and stalagmites. 
Calcite, which is the scientific name 
for all limestones, crystalizes in the 
hexagonal system. The crystals are 
usually in hexagonal prisms or rhom- 
bohedrons, Iceland spar is an exam¬ 
ple of a rhombohedron. It may be 
granular as in marble, or it may be 
compact. The cleavage is rhonibohe- 
dral. The lustre is vitreous. The 
streak is wdiite. 
The colors are w'hite or light gray¬ 
ish or yellowish, and some of the mas¬ 
sive varieties are black. If some cal¬ 
cite be placed in a test tube and a lit¬ 
tle hydrochloric acid be poured upon 
it, it will seem to boil, w'hichis caused 
