The Second Lake Ah/o/iqn/n. — Taiilov. 175 
30 feet, and it is the same for the Detroit river, except wiiei-e 
it spreads out between ishmds and becomes somewhat shal- 
lower. There is one point in each river which is nine fath- 
oms or 54 feet deep, antl for considerable distances the depth 
is seven to eight fathoms. The sounding's m lake St Clair 
show that the bottom slopes olf gradually southwestward from 
the frf)nt of the delta to three or four fathoms and seems to 
show no submerged channels except near the outlet. It ap- 
I)ears from these figures that the lake is shaHowcr than tiie 
river above and below it, except at one point near the head of 
the Detroit river, and that there are parts of each river 
that are 25 feet deeper than tiie deepest point in the lake. 
But with so much sand ])assing through the St. Clair river, 
there must have been a considerable tendency to fill up the 
bed of the river itself. No doubt some filling has actually 
taken place. But it has probably l)een mainly l)y the coarser 
sand particles which were able te resist the current that 
swept the finer grains along to the delta. The delta lias dam- 
med the stream to a small extent and so deadened the current 
slightl}'. 
Although it passes through onl}' one plane of observation, 
the line EPj has been i)Ut upon the ma|) to show where that 
isobase would be, supposing the deformation at that distance 
to preserve a parallel relation to the other lines. It is not to 
be supposed, however, that the rise, or its acceleration, nec- 
essaril}^ passes on indefinitely toward tiie northeast. It must 
come somewhere either to a fault or an anticline. A ])rojec- 
tion of the isobases towards tlu^ southeast beyoiul tlu' limits 
of the map shows that lake Ontario lies full in the track of 
the nuiin Nipissing plane, and also that EE passes right across 
the crest of the bari'ier which holds the lake up to its present 
level at Ogdensburg. (Jntai'io's shores show nuiny evidences 
<^)f a recent change of the same kind which has drowneil lake 
Erie. Along the south shore there are many drowned ba3'S 
with receiit spits and low bars, built across their entrances. 
Such are the Sodus bays, the Irondequoit and Braddock bays, 
and several estuaries along the shore west of Rochester. Mru-e 
of the sanu* kind and very st i-ikiiig in their appi-araiu/e are 
crossed by the Craiid 'I'ruiik railroad in ('anada Ix'twet-n Ni- 
agara Kails and Hamilton. 'I'he great sjjit ol' IJurlington bay 
