44 Mayden: geology of tMe provinces of tsang and 0. 
The third and uppermost division of the scarp limestone is rather 
less massive than the others, being sub-divided 
Third scarp limestone. • n • • • 
by thin flaggy layers ; it passes up into a series 
of thin-bedded limestone, at times highly arenaceous, with occasional 
sandstone bands. The sequence from the base of the third limestone 
up to the overlying ferruginous sandstone has been examined at 
various localities ; a good section is seen above the right bank 
of the Kampa stream immediately behind the fort ; others are found 
along the Kampa-Tatsang ridge which is capped, throughout almost 
its whole extent, by the ferruginous sandstone. The same series 
was examined again at Tiina, where it forms the lower third of the 
ridge behind (to the north of) the village, and is further seen on 
the southern slopes towards the eastern end of the same ridge ; to 
facilitate reference these beds may be termed the Tiina limestone. 
The last-named localities have furnished the following sequence (in 
descending order) : — 
Ferruginous sandstone 
;Grey limestone, with echinoids and brachiopods . . 5^ f^^t. 
Sandstone . . . . . . . • 3° „ 
Lithotliamnion limestone . -\ with Cyclolites regularis 
Red arenaceous limestone . > Leym., Hemtpneustes 
I Grey limestone . . J sp. and Plicatula sp. . 20 „ 
Thin-bedded limestone, with Vola sp. and echinoids 
{Holectypus sp.) 4° » 
Massive limestone with Radiolites below, Actaonella 
and CryphcBa (?) above ^ 
The lowest bed is the third scarp limestone which here, as else- 
where, is characterised by the presence of Radiolites sp. 
Towards the upper boundary of this limestone, the Rudistce dis- 
appear and are replaced by one or more species 
Horizon of Adoionella Act<£onella, the spiral (transverse) sections of 
sp. 
which are very conspicuous and form a charac- 
teristic and easily recognised horizon both at Tuna and around Kampa 
dzong (see PI. 13, fig. i). It is almost impossible to extract specimens 
from the matrix and consequently the species could not be satisfac- 
torily determined but is probably allied to A. crassa d'Orb. 
( »65 ) 
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