1897.] Fossils and Fossilization. 29 
remains which, by some accident, have been destroyed upon 
one kind of bottom, may remain represented in another that 
was not subject to the same exigencies. As Prof. Verrill re- 
marks, at the end of an enumeration of six or seven sorts of 
bottoms which carried distinctive faunas: “It must, however, 
be constantly borne in mind that very few kinds of animals 
are strictly confined to any one of these subdivisions, and that 
the majority are found in two, three or more of them, and 
often in equal abundance in several, though each species gen- 
erally prefers one particular kind of locality. In other cases 
the habits vary at different seasons of the year, or at different 
hours of the day and night, and such species may be found in 
different situations according to the times when they are 
sought.” 
The animals living along rocky shores and clinging to the 
rocks themselves or dwelling in their crevices and amongst 
the sea-weeds that clothe them, are not so apt to be preserved 
as fossils, except as they die they are swept seaward and be- 
come buried in the muds or sands of the less exposed beaches 
and flats. The occupants of the sandy beaches are provided 
with organs and have developed habits which enable them to 
secure protection against the wear and violence of the waves 
and the alternating drying and wetting of the district they in- 
habit. They penetrate the sand deeply and secure immunity 
from the accidents of the surface in the pockets, burrows and 
tubes within which they can withdraw themselves. These pro- 
tective habits render their preservation as fossils much more 
probable. The animals living in the muddy bottoms, whereon 
we may suppose a finer deposit settles, forming a tenacious 
and impalpable sediment or silt, are, in many cases, identical 
with those placed within the sandy areas, and immediately 
along the shores of a country the sandy and mud types of 
beach grade insensibly into each other so that a sandy beach 
can hardly be free from mud or a muddy margin of the land 
free from sand. And in this way the animal species found on 
one or the other accommodate themselves freely and easily 
_ to the vicissitudes and qualities of both. But the character of 
a mud bottom insures a better preservation of a shell as a fos- 
