386 



THE GEOLOGIST. 



Two very important theories liave been broaclied, as it is well 

 knoT^Ti. in reg-ard to the development and snccession of organic life 

 upon oui' planet ; the one kno^\-n as the ''progressive development 

 theoiy," derivins: each succeeding higher form by transmutation out 

 of or development fi'om a lower one : the other regarding each new 

 successive form, whatever its organic rank, as a special act of 

 creative energy. It may be veiy truly said, when we consider the 

 comparative values of these two gi-eat doctrines, that we have not 

 yet all the evidence necessaiy to decide upon theh respective merits ; 

 and. although in regard to the former, there is a natural tendency of 

 the muid to dissent from the idea of the possession by any organic 

 being of the capabihty of self- development into a higher form, there 

 ai'e so many resemblances, at least, of a series of like and further- 

 caiTied developments in the higher classes of plants and animals as 

 to make us hesitate to reject as absm^d or valueless doctrines which 

 caiTv so many specious reasons for theu^ consideration. No doubt 

 the ever and anon exerted power of creation, the placing at 

 intervals tln^oughout all the vast ages of the Past, of new and suit- 

 able forms of organisms upon om' planet, in accordance with the 

 requu^ements of its changed and altered conditions, is the more 

 popular view, as it accords more wnth our 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 progTessive development being possible -y^dthin 

 restiicted limits, while creative energy fi-om time to time supplies 

 vacuities and deficiencies and the higher gTades reqmred by the 

 more elaborated conditions of om^ 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 hiown than to enter the 

 domauis 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 — jet 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, annelides, and crustaceans (tiilobites and bivalved ento- 



