Peckham and Hall—Thomsonite from Minnesota. 127 
SiO oe i wierd Sees 46°020 
BIN simon cwreula Hemataebeian 26°717 
Beds ins tarinsaoaninniadk deel 
OAD lt iu os lw clea 6 uke ae 9°400 
BD) oS nisentc cua ke ala 0°390 
De eines a Sa meee cet Saar ene 8°75 
fe) 12-800 
99°896 
Number III.—As before stated these pebbles, when first seen, 
were supposed by us to be worn fragments of reniform prehnite, 
so common in several localities along this shore. Wesoon found 
evidence that they were amygdules; still the fact that they 
were not prehnite was not suspected until their specific gravity 
had been determined and found to be that of thomsonite, 
2°32 to 2:37. Analysis showed them to contain— 
BROS scr danke soni acting. eka mek meen 40°605 
5 aad BRED tse OMS 30-215 
OP os Sea eel ate “40 
CO eee 
i Ue RR ESS 
Ra gs Oe ae 4055 
HO fe ees S 13°75 
99°885 
_ This composition allies the mineral very closely to thomson- 
ite, so closely that, considered alone, there appears little reason 
Why the mineral should not be considered as a variety; but 
there are several notable reasons why a specific name may 
See be applied to this, as we believe, hitherto undescribed 
ineral. 
These pebbles are wholly destitute of the radiated and erys- 
talline character of other forms of thomsonite. der the 
’ 
frequently some foreign material, as a bit of copper, is a nu- 
cleus. The spherolites often occur in groups; fae numbers 
are crowded and heaped together, growing into and overlap- 
oe another, like the tridymite scales in the rhyolites of 
€xico and the trachytes of the Siebengebirge. These group- 
igs are not always spherical; sometimes they extend in long 
curving lines through the mass, following perhaps a fracture or 
. 
