112 
TENTH REPORT. 
when a subsiding coastal area of fresh marsh reached the level of the tides; 
when interbedded with the coal, it is more than possible that the deposit 
was formed upon an unstable coastal area which was oscillating up and 
down, or subject to occasional overflow caused by high tides, or severe storms, 
the thickness and character of the marine beds giving the evidence as to 
which factor should be given the greater weight. Marine beds below the 
coal may show nothing, except that there was an elevation of the surface 
before the coal began to be laid down. 
To one who has examined the salt-marsh type of peat deposit, it is apparent 
that one of the most definite arguments which can be made against the 
hypothesis that coal could have been formed in marshes covered at regular 
intervals by the tides, is that the tidal waters are heavily silt-laden, and, 
wherever they appear, leave a heavy mineral deposit behind them. It is 
equally plain that an elevation or depression of a few inches, in an area near 
the tidal level will cause an entire change in the type of plants and in the 
resulting deposits. 
It is scarcely necessary here, to call attention to the well-known and often- 
described power of preservation of the remains of animals and man, as well 
as those of plants, which peat possesses. The fact that this has been much 
more often noted in Europe than America is doubtless due to the more 
thorough development of industries based upon peat and its use as fuel, as 
well as the greater activity of geologists in working out the faunas of Pleis- 
tocene and Present times. A most excellent chance to increase the knowledge 
of the post-glacial faunas of Michigan is afforded by the present activity 
in draining marshes and ditching through peat deposits, and ever}^ large 
ditching operation should be watched, to save such vertebrate remains as 
may be uncovered. That such remains are of frequent occurrence, may 
be learned by talking with any intelligent ditcher, but it is only a rare occa- 
sion that any except the bones of the Mastodon are saved. Are we as geol- 
ogists doing our duty in neglecting the opportunities thus offered. 
A fascinating line of speculation may also be entered into as to the length 
of time which it may have taken a given thickness of peat, for example, 
measuring a period of coastal subsidence, to form. From this, it is but a 
step to conjecture as to the length of the time recorded in the accumulation 
of coal and lignite. Here, however, the knowledge obtained from the peat 
deposits is of the sort which puts the student in a very humble frame of 
mind, since he soon finds that practically each peat bed has its own rate of 
accumulation, depending upon so many factors that the problem is a most 
difficult one. if capable of solution at all. 
It is apparently certain, however, other factors being the same, that peat 
develops more rapidly in a region of heavy rainfall, than in a more arid one, 
and, correlated with this, in a cool region than in a hot one, but the number 
of feet of peat which would develop in a given period, or the length of time 
in which one foot would be laid down, it is not possible to say with any defi- 
niteness, except for a given deposit after long-continued observation. 
If these brief notes have served to call the attention of those present to a 
much neglected page of geological history, the aim of the writer is accom- 
plished. 
Ann Arbor, Michigan, April 3, 1908. 
