J. F. Campbell Collection > Parallel roads of Lochaber

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river now flows, unless the sea made a strait for the river. Lake shores
or sea margins aie clearly marked in Glen S[.iDan at low levels,
on the slopes of'' Aonacban. '''■'' That is a mound of glacial debris capped
with gravel, and I took it to be a large moraine which made a dam
when the glacier melted in Spcan Glon. But in that glen, laud has in
fact risen at least ten feet, because of sea shells at Fort William. So
the Aonachau terraces probably are sea coasts cp to GUO ferl. The
flats between Aoiiachan, and the Spraa falls, at about 300 feet
above the sea, would be good huiiling grounds for shells of the period
of 500 feet sea level, which is proved at Chapel Hall, near Airdrie. A.
bed of recent shells is under Cerpach iloss, according to a letter from
Mr. Clerk, of Kilmallie, Nov. oth, 1S77. At Spean Tails is a rock dam.
Were land now to rise there would be a dam of look at Connal
ferry, and Loch Etive would become a deep fresh lake as soon as
the rivers had washed oat the salt. Now a tidal race flows out and in
over the rock dam, with all the force and turmoil of Lachinc Rapid on
the St. Lawrence. The drift is chiefly found outride. There would be
a rock dam at the Baile Chaolais ferry, and the upper ends of Loch
Leven would become a lake by the same process, if the land were
to rise. A great mass of terraced shingle about Corran and Corpach in
Loch Linne might be taken for the remains of a dam of detritus, to ac-
count for sea margins by lakes at the upper end of Loch Linne and
of Loch Eil. Loch Lochy and all the lakes which now are joined arti-
ficially by the Caledonian Canal, have large dams of stratified shingle
at their ends. Gleu Gloy belongs to that .system. Glen Gloy lias
"parallel roads " in it, at 1,1G5 feet, and it is said that there also are
lake shores. The dam is wanting at the mouth of Glen Gloy, and there
is no remnant of it in Loch Lochy or in Loch Linne. If the great glen
were full of ice, there might be an ice dam at the rnouth of Glen Gloy.
If there were dams in Loch Linne, and at Inverness, aud elsewhere, all
the lakes in the great glen might join in one, but the sea at 1,000 feet
higher, or the land a thousand feet lower, would account for terraces
in Gleu Gloy and Lcchaber, and in Glen Spey without local dams.
The American coast would be the dam. Dams of drift are at both ends
of Loch Ericht, and they are like the rest of these dams, which are at
all levels up to I,lo.j or 1,200 feet. So far as I know these dams, either
they arc the lips of rock basiuSj or they are moraines washed by water.
They are made of boulder clay capped with stratified sands and gravels.
With so many dams at so many levels, it was natural to account for the
Lochaber terraces at first by dams like the rest. But there is no rem-
nant of a dam of this kind large enough to account for the beach marks
in Glen Roy by a lake held by a dam of detritus. Nevertheless dis-
tinguished geologists still believe in lakes dammed by " detritus," which
dams have been somehow removed.
Slraits. — The sea is always building dams in " Cols"' which are within
reach of the sea. The nature of Straits or Sounds I ha-se learned
amongst the Scotch islands. The outer Hebrides extend from u6M5
N. Lat., to 58°.30. Sounds between the islands are in fact " Cols ''
' Aon — one. Aonach— a solitude ; a lone hill. Aonaclian — lone hillock.