Fo Dea RE 
357 
THURSDAY, FEBRUARY 16, 1882 
AVPOTHETICAL HIGH TIDES 
| igo his interesting lecture entitled “A Glimpse through 
the Corridors of Time,” recently published in 
NATURE, Prof. Ball, accepting Mr. George H. Darwin’s 
view—that the moon was once part of the earth’s mass, 
and after separation long revolved much nearer to us 
than now—estimates that when 40,000 miles distant she 
produced tides 216 times greater than the present, and 
advances the theory that these high tides have been the 
most powerful agents in producing changes on the earth’s 
surface. He further presents this theory to geologists as 
a solution of some of their most difficult problems. 
All this is exceedingly interesting if true. There can 
be no question that a tide of six hundred feet sweeping 
over all shores and lowlands twice a day would be a most 
powerful destructive and creative engine ; and it may be 
conceded at once that its potency in remodelling the 
earth’s surface would far surpass any agent of change 
now in action. Hence we may fairly infer that if such 
tides had prevailed in former times they should have left 
behind them universal and indisputable evidence of their 
existence. 
Having studied with some care the geological record 
in places where it is as nearly complete as anywhere, I 
must say that I fail to find there any traces of the action 
of these stupendous tides pictured to the imagination by 
Prof. Ball. On the contrary the whole of that record, 
from the Archzean to the present time, offers evidence 
opposed to such a theory as he proposes. 
Of what took place before the Laurentian strata were 
deposited we can gain no knowledge from the rocks, 
because these are the oldest known. We can only say 
that they are aqueous sediments of which the materials 
were derived from pre-existent land. Though much 
metamorphosed they are plainly the prototypes of the 
sandstones, shales, and limestones of later formations, 
and, we may fairly conclude, were deposited under like 
conditions. In the granites of the Laurentian we appa- 
rently have representatives of the coarser sediments 
formed along shores; the slates are the clays of ancient 
times, the wash of the land deposited in quiet waters off 
shore, while the marbles—which in some places form a 
considerable portion of the Laurentian series—are un- 
doubtedly organic sediments that accumulated in quiet 
water, deep or shallow, by the slow processes of growth 
and decay of animal structures. Graphite, the product 
of plant life—probably fucoidal—exists in large quantities 
in the Laurentian rocks, and they contain enormous beds 
of iron ore which must have been accumulated by the 
aid of organic matter. Hence we may say that in the 
Laurentian age life was abundant, and much of this was 
littoral life, and that the vital unites with the physical in 
opposition to the high tide theory. 
The Huronian series consists mostly of slates, quartz- 
ites (sometimes ripple-marked), and beds of iron ore, all 
shore and shallow water deposits speaking of quiet times 
and no high tides. 
The Cambrian rocks are but imperfectly shown on the 
eastern side of the North American continent, and we 
VOL. Xxv.—-No. €42 
will not stop to inquire minutely into the circumstances 
of their deposition, We may say, however, in passing, 
that they contain no really coarse material, and are all, 
so far as is known, the deposits of quiet waters. 
In the Lower Silurian series, which is here remarkably 
complete, we have a record that tells with great clearnes 
the physical as well as the vital history of the continent 
in that age. 
The Potsdam Sandstone, the base of our Silurian, is an 
old beach spread over large areas of pre-existent land by* 
a slow and quiet subsidence, and the invasion of the sea 
The Laurentian highlands, the Adirondachs, the Archean 
area south of Lake Superior, formed the shores of this 
sea ; and the Ozark Mountains, the nucleus of the Black 
Hills, &c., were islands in this sea, each with its shore 
line. The old Potsdam beach is now exposed, and has 
been examined in hundreds of localities along a line of a. 
thousand miles or more, and there the ancient sea margin 
can be followed as easily and certainly as we can now 
meander the line of the Atlantic coast. We everywhere 
find the history of the old beach written with unquestion- 
able accuracy and in great detail. The strata are fre- 
quently ripple-marked and sun-cracked, their surfaces are 
covered with the interlacing casts of seaweeds, the sand 
is bored in every direction by annelids, and is full of the 
fragmentary or complete shells of the beach-loving lin- 
guias. This record not only includes no traces of extra- 
ordinary high tides, but is full of positive evidence that in 
the beginning of the Silurian age no tides much higher 
than at present swept the Atlantic coast of North 
America. 
Above the Potsdam sandstone is spread a great sheet 
of organic material, the Trenton limestone group, im: 
places a thousand feet thick, the deposits of quiet waters, 
and composed almost entirely of the hard parts of animals 
which inhabited them. As we approach the old shores 
these limestones become more earthy, and in places they 
abut directly against Laurentian cliffs, which supplied so. 
little mechanical material as to form but a trifling per- 
centage of the deposit made. Here we are on the old 
shore line, and are surrounded with evidence of the slow 
and quiet accumulation of material, and the entire absence 
of any indication of tidal action greater than that of the 
present day. 
The same phenomena teach the same lesson in the 
records of the Upper Silurian, Devonian, and later geo- 
logical ages. In the Devonian rocks we have another 
witness against extraordinarily high tides, for here are 
coral reefs rivalling those now forming in the tropical 
seas. Unless the reef-building polyps of the Devonian 
age were altogether different in habit from those now 
living, these coral reefs must have been formed in water 
less than two hundred feet in depth. Here high tides 
would have wrought the rapid destruction of the whole 
race of reef-building animals, at the ebb exposing them 
to the air for hours, and at the flood burying them too 
deeply for their continued existence. Nearly the same 
thing is taught by many of our great limestone beds. 
They are largely made up of mollusks, corals, &c., which 
inhabit a littoral zone, and it is evident that a tide 
hundreds of feet in height, sweeping to and fro over that 
zone, would have rendered it uninhabitable by them. 
The sea-weeds now living in our oceans, chiefly occupy: 
R 
