38G 
THE GEOLOGIST. 
Two very important theories have been broached, as it is well 
known, in regard to the development and succession of organic life 
upon our planet ; the one known as the " progressive development 
theory," deriving each succeeding higher form by transmutation out 
of or development from a lower one ; the other regarding each new 
successive form, whatever its organic rank, as a special act of 
creative energy. It may be very truly said, when we consider the 
comparative values of these two gi-eat doctrines, that we have not 
yet all the evidence necessary to decide upon their respective merits ; 
and, although in regard to the former, there is a natural tendency of 
the mind to dissent from the idea of the possession by any organic 
being of the capability of self-development into a higher form, there 
are so many resemblances, at least, of a series of like and farther- 
carried developments in the higher classes of plants and animals as 
to make us hesitate to reject as absurd or valueless doctrines which 
carry so many specious reasons for their consideration. No doubt 
the ever and anon exerted power of creation, the placing at 
intervals throughout all the vast ages of the Past, of new and suit- 
able forms of organisms iipon our planet, in accordance with the 
requirements of its changed and altered conditions, is the more 
popular view, as it accords more with om' preconceived notions of 
the unceasing watchfulness of the great Creator. 
Perhaps the truth may be found to be a modification of both, a 
certain amount of ^progressive development being possible within 
restricted limits, wliile creative energy from time to time supplies 
vacuities and deficiencies and the higher grades required by the 
more elaborated conditions of our globe. 
Be all this as it may, our duty is plainly to present facts as we 
find them, and rather to define what is truly Icnoicn than to enter the 
domains of speculation. One important fact is even now evident — 
that while apparently in neither vegetable nor animal kingdom do 
we start with the lowest group — while seemingly we begin neither 
with the protozoan nor the diatom — yet every successive great 
geological age has presented us with some marked successive 
development of, or the production of some more highly organized 
condition of animal- or vegetable-life. In the Lower Silurian strata 
molluscs, annelidcs, and crustaceans (trilobites and bivalved ento- 
