95 
sponge spicules occur as a deposit in the upper part of the alluvial 
material filling the Princess Royal "Deep Lead/’ forming a bed 
said to he over ^35 feet in thickness. Dr. Hinde’s conclusion after 
examining the spicules was that the deposit was formed in the 
open ocean at some distance from a coast-line and probably in 
considerable depth of water, and he thinks them likely to be post- 
cretaceous in point of age. 
The “deep leads” all over the State arc old valleys which 
have been filled up before the present lakes were formed, and the 
Princess Royal sponge spicule deposits would go to indicate that 
they became filled u]) during a subsidence which brought the sea 
so far inland that the present site of Norseman was in deep water 
well out from the coast, d'his might perhaps have been during 
the time of the Cretaceo-Tertiary subsidence, which resulted in the 
laying down of the Encla limestones, and if this date could be 
established for the case of the Princess Royal L)eep Lead, it would 
probably apply generally to all the other deep leads of the State 
which are quite similarly buried under lake flats. It would not 
necessarily follow, however, that marine sediments should be ex- 
pected to be found in all of these, as the first effect of a movement 
of subsidence would be to start the filling up with drift of all the 
valleys near the coast long before they became submerged under 
sea waters. The material found filling them as a matter of fact 
appears generally to be of sub-aerial origin and not marine. The 
Princess Royal valley appears to have remained open however, and 
to have become deeply submerged, giving the opportunity for col- 
lection in it of the deep-sea deposit of sponge remains. The more 
littoral shell-beds might have been formed at almost any period dur- 
ing this movement of submergence and subsequent emergence of 
the land, but probably at either an earlier or later stage than the 
spicule beds, and if the species i)rove to be altogether more recent 
than the Kucla limestone period, as appears to be the opinion form- 
ed at present, it would be probable that they belong to a Post- 
Tertiary repetition of the process of submergence and subsequent 
elevation much later than the Cretaceo-Tertiary one in which the 
Eucla limestones were formed, f'rom their position they look like 
littoral deposits of an arm of the sea, occupying the site of Lake 
Cowan to, a dejilh at least feet above its present level, and seem 
most likely to belong to the last period of the connection of the 
lake with the sea before the continuance of the elevatory move- 
ment cut the former off from the latter, and raised it up some 900 
feet. The presumiHioit would then he that the deep leads generally 
are mostly likely of an age between the times of the Cretaceo- 
Tertiary subsidence and elevation which gave us the Eucla lime- 
stones and a subsequent similar Post-Tertiary down and up move- 
ment which gave the more recent Norseman beds. The leads would 
represent stream channels in the land surface existing between the 
two periods of subsidence. 
