256 Geological Systems—Geological Maps, &c. 
as much ata loss to conceive where it begins, as I am to coti- 
jecture where it isto end. It seems to be composed in part 
of Werner’s alluvial and secondary, but the limits to which it 
is confined appear to me undefined and speculative, eer 
on the distinction between depositions accumulating on the 
pataen of deep water and those rolled and left on the seadens 
of either a sea or lake—a pes ai difficult to make at this 
distance of time from the operati 
If sand or rolled masses are ne criterion, = the transition 
puddings and sand-stone would become tert 
able at present to investigate the grounds of thes speculative 
' opinions, and no reasoning but that elicited by the stroke af 
e hammer can throw light on the subject. 
CHATOYANT FELDSPAR. 
Since I arrived in this eity, I am induced, on inspecting 
specimens of the feldspar in granite called moon-stone, and 
of the Labrador feldspar, both of which present changeable 
colours, to conclude that the phenomena are, in both cases, 
caused by t Itration of water under crystalline layers 
which form the _— and 1 am confirmed im that opinion 
by fi the river below Shafhausen a granite “sca 
the feldspar of which had the same properties as the 
for feldspar. 
Se t | 
