528 
Proceedings of the Royal Soeiety 
of our chalks, greensands, sandstones, conglomerates, shales, marls, 
and other sedimentary formations. Such formations as certain 
tertiary deposits of Italy, Kadiolarian earth from Barhadoes, and 
portions of the Chalk where pelagic conditions are indicated, must 
he regarded as having been laid down rather along the border of a 
continent than in a true oceanic area. On the other hand, the 
argillaceous and calcareous rocks, recently discovered by Dr 
Guppy, in the upraised coral islands in the Solomon group, are 
nearly identical with the volcanic muds, and probably also with the 
Pteropod and Globigerina oozes of the Pacific. 
Eegions situated similarly to enclosed and shallow seas and the 
borders of the present continents appear to have been, throughout 
all geological ages, the theatre of the greatest and most remarkable 
changes ; in short, all, or nearly all, the sedimentary rocks of the 
continents would seem to have been built up in areas like those 
now occupied by the terrigenous deposits, which we may designate 
‘‘ the transitional or critical area of the earth's surface." This 
area occupies, we estimate, .about two-eighths of the earth’s surface, 
while the continental and abysmal areas occupy each about three- 
eighths. 
During each era of the earth’s history, the borders of some lands 
have sunk beneath the sea and been covered by marine sediments ; 
while in other parts the terrigenous deposits have been elevated 
into dry land, and have carried with them a record of the organisms 
which flourished in the sea of the time. In this transitional area 
there has been throughout a continuity of geological and biological 
phenomena. 
Prom these considerations it will be evident that the character of 
a deposit is determined much more by distance from the shore of a 
continent than by actual depth] and the same would appear to be the 
case with respect to the fauna spread over the floor of the present 
oceans. Dredgings near the shores of continents, in depths of 1000, 
2000, or 3000 fathoms, are more productive both in species and 
individuals than dredgings at similar depths several hundred miles 
seawards. Again, among the few species dredged in the abysmal 
areas furthest removed from land, the majority show archaic 
characters, or belong to groups which have a wide distribution in 
time as well as over the floor of the present oceans. Such are the 
