480 Scientific Intelligence. 
“Onondaga Salt group,” has the following dimensions, according 
to a recent letter to one of the editors received, along with an 
excellent stereoscopic photograph, from Mr. J. G. Far argo of Bata- 
via: height 12 feet; width of base 20 feet, of neck 8 feet, of top 14 
feet. It is underlaid a about 40 feet of drift, beneath which is 
the poate ater 
3. O dof distinguiching the different Feldspars by 
means of nibble an properties ; (Extract from a letter from M. 
DesCtoizeavx, dated Villen-sur-mer, July, 3d, 1875 Fa 
This method can be applied to all the feldspars, and gives a Be 
easier means of distinguishing them than those de soribed in my 
last memoir (this Journal, III, ix 
easiest cleavage [ ab and smooth enough to be homogeneous in all 
its parts. Similar sections obtained from crystals or lamellar 
masses of albite, oligéclane, labradorite, and the majority of those 
= damage show hemitropic bands, more or less close together, 
anged along the plane parallel to the second cleavage [9*]3 
for orthoclase and microcline in i ot crystals, two sections placed 
in opposite directions serve to produce the same effect. These 
sections are thus brought between ao crossed Nicols of a polari- 
zation-microscope. 
(1.) For orthoclase the maximum extinction takes place when 
the two sections are parallel to their plane of —- the edge 
of the same plate of the macle - n e), a ; 
eign the two plates of the m (microcline in bands), or 4 
9° 27' between the adjoining east s (microcline and ort 
lane of com- 
show at the same time an extinction oblique to the 
A Fa to this 
position, pie sx the microcline, and one par 
plane for the orthoc ‘ 
(3.) For eae me ectinsGion between two bands takes place 4 
an angle of 6° 
(4.) For tsb: the extinction is simultaneous in bee 
bands, and when the plane of composition coincides with the plan 
of polarization of the polariscope, it shows that the structure 18 
homogeneous. ’ 
65.) For labradorite, the extinction takes place at 10° 2 
ge pig? the 
axes cuts the base along a line making with the e 
following angles 
0° in orthoclase and microcline. 
ae 27° in mi 
° 16’ in albite 
° 12’ in labradorite. 
