144 
WATER AGATES. 
In one of the recent issues of ‘*The 
Oregon Naturalist’’ occured a note in re- 
gard to ‘‘water agates’’. It may be that 
your readers would be interested in their 
history. 
‘‘Water agates’’. more properly amygd- 
oles, are always found in vesicular lava, 
basalt and the like, and are composed of 
quartz. It often occurs that they are hol- 
low and frequently contain water made visi- 
ble by the presence of a bubbleof air or per- 
haps some other gas. Other soecime1s 
contain no water and still others are solid. 
An observing visitor of the Orezon shore 
line will have noticed that all the rocky 
headlands are composed of hard black rock, 
frequently showing the familiar columnar 
structure. This rock is basalt. The parts 
of the shore between these promontories 
are composed of sandstone, conglomerates 
and other forms of sedimentary rocks. 
A cateful studv of tke zones of centact 
between the sedimentary rocks and the 
basalt will show how the latter got there. 
It will be seen readily that the stiff 
tava has been pushed up in more or less 
vertical fissures and by its heat has 
changed or metamoiphcsed the adjacent 
rocks, changing their structure for some 
distance from the basalt. This loose 
gravelly sandstone may be cemented 
together into a firm mass. 
Now every body knows that lava may 
have cavities or vesicles in it. These are 
sometimes large and few, or may be nu- 
merous and small. Now these cavities 
are the birthplaces of amygdoles. Chem- 
ists tell us that silica - or quartz — is solu- 
ble inalkaline warm water. Lavacontains 
silica and various alkalis, and rain falling 
upon these lava dykes dissolve .a part of 
the alkali and at the same time becomes 
heated — for these hard black lavas are 
those which have cooled slowly. This 
warm alkaline water then dissolves silica 
and fills these cavities andthe whole mass 
THE OREGON NATURALIST. 
cools, the quartz is deposited in bands and 
crystals, sometimes filling the cavities and 
sometimes leaving a hollow containing 
water or empty. This is the history of all 
our beautiful banded agates. These are 
often colored by oxide of iron, etc. - 
Not infrequently it happens that clams, 
groups of crystals and other objects are 
embedded inthe viscous lava, and are de- 
stroyed by the heat, not however until 
they leave their record in the form ofa 
claw shaped cavity or one of some other 
form. These cavities too, may be filled 
with quartz, often colored, and give us 
the so called ‘clam pseudomorph’ they are 
not fossil clams but merely casts of clams 
made after the original was destroyed. 
One often finds black pebbles contain- 
ing small white nodules These are peb- 
bles of basalt containing small amygdoles. 
The word amygdole is derived from the 
Greek word signifying an ‘almond’ and 
are so named because these vesicles are 
often almond shaped and the filled in ma- 
terial will be an ‘almond’ or amygdole. 
FRANCIS E. LLOYD, 
Prof. of Biology, Forest Grove, Ore. 
PRESERVATION OF OPHIDIANS. 
In a recent work on taxidermy the reader is 
directed to remove the skin ofa snake by making 
a longitudinal incision along the ventral surface, 
then to sew up the skin and stuff it with cotton. 
I do not know what is expected of a taxi- 
dermist, but as a naturalist I would not find 
this method very satisfactory. 
In some snakes the anal plate, the epidermal 
scute anterior to and covering the vent, is entire, 
while in others it is divided, This difference is 
of great importance in identifying serpents. 
Sometimes the plates on the ventral surface of 
the tail, post abdominal scuteilae, Prof,Cope 
would call them, are s.ngle or entire and some- 
times they are divided or in pairs and this dis- 
tinction is of value in classification, ' 
With certain snakes, as with a common variety 
of the Matrix stfezon, the ventral surface is 
