22 GEOLOGICAL MEMOIRS. 
transmitted light had often a brownish and yellow, sometimes a red- 
dish-brown or black colour. Among these are cellular particles per- 
fectly similar to pumice-stone rubbed down ; and often small erystals, 
which appear like pyroxene erystals, and show a greenish colour, but 
many are colourless. In form they are constantly prismatic, with an 
obtuse acumination. Consequently molten, baked, and merely me- 
chanically divided siliceous portions with crystals form the chief part 
of the mass, which is predominantly vitreous. 
Besides these inorganic substances, there is found in each portion 
as large as a pin- -head (4-4 of a line) a trace of distinctly organized 
matter in the form of small siliceous shells of animals or fragments of 
plants (Phytolitharia), and also carbonized soft parts of plants. 
In fifty accurate analyses of such small portions, nineteen distinct 
organic bodies, some in several specimens, have been recognized, as 
in the following table :— 
A. PoLYGASTRICA. 
. Achnanthes exilis ?..........000- — 
. Arcella hyaiina ..iesssecsesc.see = 
wulpraris 2 gcc5 teced owas. canes = 
. Difflugia areolata  .........200... — 
A cr <P ee ee - 
Ors 0 DO ks 
+++ | 
B. PHYTOLITHARIA. 
6. Lithasteriscus tuberculatus ...| — 
7. Lithodontium furcatum ......... _ 
8 MASUR. 3 ee tutpeceoe eee nee _ 
9. WHlaLyoOuon ~ 25 elioe.sests--- + 
10. rostrata 7. 2k > ee — 
_ 
14, wnidentatuit” .3...,....,5.5 =_ 
15. Trabétdia’” WiS..F: = 
C. Doubtful Organic Siliceous particles. 
=} 5 
Li+t+++i +++ 
Gala ee a OU 
3 
1 
1 
1 
2 
2 
0 
1: 
1 
1 
El bel 3 &: 
a a) 
D. Soft parts of Plants carbonized. 
Se. Hares Of IWR opera een 
19. Cellular tissue of plants ......... 
lo 
++ 
“te | 
bo 
Of the fifty analyses, 2 referred to No. I.; 13 to No. I.; 23 to 
No. III.; and 12 to No. IV. All the packets exhibited similar or- 
ganic mixtures, but they were fewest in No. IV., which is the 
coarsest. On washing a portion of No. II. I found the finer parts 
richer in organisms. On the whole, no portion of No. II. as large as 
a pin-head was found without organic matter. In No. IIL., of 20 
such portions, 7 were barren. The number of times that each of the 
above forms recurred is given in the fifth column of the table. 
