69 
Age of the Rocks (Nos. 5 to 57). —There can be very little doubt, from 
the presence of several characteristic fossils, and the general faunal aspect, 
that the series of specimens from the three foregoing localities are of 
Silurian (Yeringian) age. As is usual in the uppermost Silurian beds of 
Victoria, there is here present a fair number of forms elsewhere regarded 
as Devonian. 
THE FOSSILIFEROUS LIMESTONES AND CONGLOMERATES OF THE 
THOMSON AND TYERS RIVERS AND MARBLE CREEK, GIPPS- 
LAND.—(COLLECTED BY Mr. A. E. KITSON.) 
V 
Thomson River Limestones, (no. 40 on locality map.) 
Lithological Characters .—The specimens from the Copper Mine, Thom¬ 
son River, numbered 204-210, and 65, are compact, sub-crystalline, fossil- 
iferous limestones. They are of a grey colour when freshly fractured, 
and weather to a rusty-brown on rough surfaces which have been long 
exposed. These limestones are principally of organic origin, and, owing 
to the preponderance of crinoid remains, are typical crinoidal limestones. 
The bright cleavage surfaces of the original crystalline components of the 
column and other portions of the crinoid-skeleton impart a crystalline 
appearance to this limestone, which is, however, different from the structure 
seen in highly metamorphosed or statuary marble, where the constituent 
grains do not show any outlines of organic fragments. 
On the weathered surfaces of the Thomson River limestones, columns 
of a large form of crinoid are conspicuous, the diameter of the stems often 
measuring 13 mm. Microscopic sections have been made from Nos. 207 
and 208 (slices Nos. 1019 and 1008), and these, on microscopic examination, 
yield further evidence of organic remains than can; be obtained by a 
superficial inspection of the rock. Under the microscope it is seen that 
the cementing portion of the limestone is now in the condition of finely 
crystalline calcite. That the rock has undergone’ certain dynamo-meta- 
morphic changes is well shown by the strong curvature of the rhombohedral 
cleavage developed in the calcitic plates composing the crinoid joints; and 
in a few cases the rock has been distinctlv “ sheared.” 
No. 207, in thin section, shows the rock to be largely of organic origin, 
crinoid remains being abundant; the whole is cemented by a finely crys¬ 
talline calcitic paste, more or less impure, and occasionally graphitic. The 
only alteration this rock has undergone is a little secondary crystallization 
of the calcite, which tends to obscure the structures of the organic con¬ 
stituents. In the microscope slide of this rock the following organisms are 
present:—Numerous crinoid remains, carapaces of ostracoda (sub-oval in 
section), and an example of the genus Fistulifrora .—(See PI. II., fig. 3.) 
The slice of No. 208 is also crowded with organic remains, chieflv 
crinoids, the other fossils present being rendered obscure by the large 
amount of shearing in the rock. The original cellular appearance charac¬ 
teristic of all echinodermal structure is only seen here and there as a 
minute stippling of dark particles. In both this and the former slidff a 
small amount of crystalline quartz i s seen disseminated through the rock; 
and where the crinoid plates have been fractured they show recementation 
by finely crystalline calcite (see PI. I., fig. 1). 
