Kin AHA N — Killary Bay and Slieve Partry Silurian Basin. 721 
Tip to consolidate the materials ; while subsequently, during carriage, 
the materials are again shaken. Usually during the erection of any 
large structure some barrels and sacks of cement are spoiled" ; that 
is, become stone, and under such circumstances in them are developed 
structures similar to those found in limestones. In a barrel filled with 
the shovel there are layers, in each of which there are more or less 
oblique and spheroidal structures, due to the shakings ; and in all is 
an irregular cleavage due to shrinkage. Sacked cement has in general 
only a spheroidal structure, with lines that seem to be incipient 
cleavage. 
In many ordinary limestones, but invariably in metamorphosed 
limestones, there are similar structures ; but in the latter usually they 
are much modified on account of the vicissitudes the rock has under- 
gone. In the natural limestones there are also the silicious and argil- 
laceous layer and parting of the original accumulation ; but in old 
plaster and dead cement any partings, or traces of partings, must be 
due to the leaching out of the non-limy materials. 
Such irregular structures in the metamorphic limestones are claimed 
to be the result of shearing and upthrusting. Why so I cannot con- 
ceive, when similar structures are conspicuous in unsheared rocks. In 
the metamorphosed rocks, however, such structures ought to be much 
more conspicuous, as leaching out and other molecular changes, neces- 
sarily, would considerably augment and develop them. Upthrusting 
would tend to make the contortions more prominent, while the shear- 
ing in places would break up the continuity of the layers and parting, 
leaving the remains scattered about in the limestone. The latter 
often have an appearance like inlying pebbles of chert and mica 
schist ; for which, by some observers, they have been mistaken. There 
are also the nodules and lentils of endogenous granite, that have been 
said to be inlying pebbles by some ; and by others, portions of veins 
broken up by shearing. They, however, never were either, having all 
the characters of pegmatite or endogenous granites. 
The above structures are more or less conspicuous in the meta- 
morphic limestones south of the Clifden and Oughterard road, while 
a little north of that road, about a mile and a-half north-east of 
Clifden, near Lough Cashleen, in very slightly altered limestones, 
there are layers and nodules of chert similar to those found in ordinary 
Silurian and Ordovician limestone. 
The well-known Connemara serpentines {ophiolites and opliical- 
cites, Sfc), all of which occur in the country north of the Clifden and 
Oughterard valley, are stated to have originally been pickrites, or an 
