MARINE AND ESTUARINE DIATOMS. 
225 
or the ocean, and notwithstanding their minuteness, may give 
rise in time to silicious deposits of vast extent. The material 
thus formed is known as Tripolite or Infusorial Earth, and 
several very interesting beds of it occur in New Brunswick, 
which will be treated of in a later article. But it is in the ocean 
that the results of Diatom growth and accumulation are most 
remarkable, it having been ascertained through the explorations 
of the Challenger and other expeditions, that large portions of 
the ocean’s bed are made up of little else. Sir Joseph Hooker, 
during the expedition of the Erebus and Terror to the Antarctic 
seas, found a bank of Diatoms 400 miles long and 120 miles 
broad, in latitude 6o° S., and the later investigations of the 
Challenger indicated that what is probably the same bank, really 
has a length of not less than 1,700 miles. The naturalists of the 
latter exploration were also led to believe that a great zone of 
Diatoms, or rather of Diatom-ooze, surrounds the South Polar 
regions between the Antarctic circle and the latitude of 40° S., 
which is estimated to cover nearly 11,000,000 square miles, 
while a smaller patch in the North Pacific covers about 40,000 
square miles. 
Considering the indestructibility of the skeletons of Diatoms, 
it is not to be wondered at that these should also occur in a 
fossil condition. As a matter of fact they are found in various 
formations as far back as the Cambrian era, but are most 
abundant in the Mesozoic and Tertiary periods, then forming 
deposits comparable with those of the existing oceans. The beds 
of Tripolite, already referred to as occurring in New Bruns- 
wick, are of this nature, and though doubtless still in process of 
formation, may have begun their growth in the Pleistocene or 
even in earlier periods. But of these we propose to speak more 
fully on a later occasion. 
I must mow close this introduction by a few remarks upon 
the collection, preservation and study of Diatoms. 
I have already indicated the places in which Diatoms are to 
be sought. It is a good plan to carry a number of small 
collecting bottles, which, by closing with the finger and inversion, 
