JSTorth American In/erc/hicial Deposits. — Upham. 289 
recede rapid]}" northward and be immediately followed by 
fertility of vegetation and of animal life. 
At a somewhat later time than that represented by the To- 
ronto and Scarboro' fossiliferous modified drift, when the ice- 
sheet had so far receded as to uncover the Ottawa and St. 
Lawrence valleys, which then became filled with the far more 
extensive Gulf of St. Lawrence to lake Champlain, almost to 
the mouth of lake Ontario, and to Allumette island of the Ot- 
tawa river, 75 miles above the city of Ottawa, the presence of 
a flora including forests, and a marine fauna, nearh^ like 
those of to-day in the St. Lawrence region, is known, as so 
fully described by Sir William Dawson in his recent work, 
''The Canadian Ice Age," and in his man}^ earlier papers, by 
their remains in the Leda clays and Saxicava sands, deposited 
during the short interval between the glacial retreat and the 
reelevation of the land from its Champlain subsidence. 
In a limited sense the Toronto fossils may be called inter- 
glacial, as the term is used in the present paper, since they lie 
between deposits of glacial drift; but they seem better re- 
ferred to moderate oscillations of the ir-e boundary, during its 
general retreat after the lowan stage, that is, to a time dur- 
ing the Wisconsin or moraine-forming stage, ratiier than to 
the distinct glacial epochs which Coleman infers from them. 
Both these beds and the richly fossiliferous Leda clays, which 
last everywhere overlie the latest glacial drift, may be re- 
ferred to the Champlain or closing epoch of the Ice age: and 
they both testify of the close sequence of a warm clinuite, with 
luxuriant plant and animal life, immediately after the ice re- 
treated. 
Professor Chamberlin, writing of these Tt)ronto and Scar- 
boro' interglacial fossiliferous beds since ni}^ study as given in 
the foregoing paragraphs but previous to its publication, has 
referred them provisionally to the interval between his lowan 
and Wisconsin glacial drift formations; and he thinks that a 
readvance of the ice-sheet to the nu»st western and southern 
of the Wisconsin series of marginal moraines drove out tlie 
mollusk species which were mentioned as now limited in their 
geographic range to the Mississippi river basin.* Concerning 
this hypothesis, it is to be renuirked that we have nowhere 
*"The Great Ice Age," third ed., 1894, pp. 705-769. 
