Charles Schuchert— Historical Geology, 1818-1918. 101 



being the oldest; that a distinct succession of animals and 

 plants had inhabited the earth during the different geological 

 periods; and that the order of succession found in one part of 

 the earth was essentially the same in all. More than 30,000 new 

 species of extinct animals and plants had now been described. 

 It had been found, too, that from the oldest formations to the 

 most recent, there had been an advance in the grade of life, both 

 animal and vegetable, the oldest forms being among the simplest, 

 and the higher forms successively making their appearance. 



It had now become clearly evident, moreover, that the fossils 

 from the older formations were all extinct species, and that only 

 in the most recent deposits were there remains of forms still 

 living . . . Another important conclusion reached, mainly 

 through the labors of Lyell, was, that the earth had not been 

 subjected in the past to sudden and violent revolutions ; but the 

 great changes wrought had been gradual, differing in no essen- 

 tial respect from those still in progress. Strangely enough, the 

 corollary to this proposition, that life, too, had been continuous 

 on the earth, formed at that date no part of the common stock 

 of knowledge. In the physical world, the great law of 'cor- 

 relation of forces' had been announced, and widely accepted; 

 but in the organic world, the dogma of the miraculous creation 

 of each separate species still held sway." 



Evolutionary Period. — This period begins with 1860 

 and the publication of Darwin's Origin of Species (late 

 in 1859). It is the period of modern paleontology, and is 

 dominated by the belief that universal laws pervade not 

 only inorganic matter, but all life as well. Louis Agas- 

 siz had been in America fourteen years when Darwin's 

 book appeared, and his wonderful influence in bringing 

 the zoology of our country to a high stand and the 

 further influence he exerted through his students was 

 bound to react beneficially on invertebrate paleontology. 

 Shortly after the beginning of this period, or in 1867, 

 Alpheus Hyatt, one of Agassiz's students, began to apply 

 the study of embryology to fossil cephalopods, showing 

 clearly that these shells retain a great deal of their 

 growth stages or ontogeny. This method of study was 

 then followed by R. T. Jackson, C. E. Beecher, and J. 

 P. Smith, and has been productive of natural classifica- 

 tions of the Cephalopoda, Brachiopoda, Trilobita, and 

 Echinoidea. 



The dominant invertebrate paleontologist of this 

 period was of course James Hall, who described about 

 5000 species of American Paleozoic fossils. He also 



