SECTION IV. 1883. Azo] Trans. Roy. Soc. CANADA. 
VI.—On a Method of Distinguishing Lacustrine from Marine Deposits. 
By G. F. MATTHEW. 
(Read May 25, 1883. 
While examining samples of the recent deposit of the Torryburn Valley, near Saint 
John, N.B., the writer had occasion to test the specific gravity of the layers from different 
parts of the formation, and found that there was a constant relation between the weight 
and the physical conditions under which the several parts of the deposit were formed. 
The most decided change in the specific gravity was noticeable, where marine gave place 
to fresh-water clay ; and again, where the latter were succeeded by lake peat and fresh- 
water marl. 
The lacustrine beds of this formation were deposited in a sheltered basin surrounded 
by hills, and all the conditions were favourable to the preservation of minute organic 
matter. The underlying clays which are undoubtedly marine can easily be recognized as 
such by the presence in them of such shells, as Mya truncata, Mytilus edulis, Macoma Groen- 
landica, Balanus crenatus, &c. The over-clays have no such shells, though rare fragments, 
which may have belonged to Mytilus edulis and Mya truncata, are occasionally found in the 
lower layers near a point where a brooklet enters the lake: these, however, appear to be 
accidental, and to have been introduced into the lacustrine clay by the washing away of 
the marine clay along the course of the stream after the elevation of this clay above the 
sea-level. 
In the texture and general appearance of the clay at the border of the present lake 
there is very little difference between that which is marine and the later clay of fresh- 
water origin; but, on levigating the latter, a considerable quantity of finely divided 
organic matter was obtained, and was evidently an important constituent. The lessened 
gravity of this part of the deposit can thus be accounted for, long before the presence of a 
lacustrine fauna gives the more obvious proof of a change from marine to lacustrine condi- 
tions. This, in the case of the Torryburn clays, was not obtained until about one twelfth 
of the whole fresh-water deposit had been passed through (from the bottom upward) ; 
here, however, it was but the slightest indication of molluscan life which might easily 
have been overlooked, and the molluscan fauna did not appear in force lower down than 
one-eighth from the bottom. 
On investigation of the finely divided organic matter of the lacustrine clay, it was 
found to be almost entirely composed of cellular tissue and, where this most abounds, the 
clay possesses a dark olive-gray hue. The original colour of the unchanged argillaceous 
sediment, as may be seen both in the marine clay and in such parts of the fresh-water clay 
as are most deficient in organic matter, having been reddish brown. Twigs, leayes, and 
small branches of trees and shrubs are scattered through the lacustrine clay, but do not 
seem to haye had much influence in altering its general colour, the elimination of the red 
colour being apparently due to the finely divided organic matter. It seems highly probable 
