DKY LAND IN GEOLOGY COLEMAN. 257 



sound of the surf, he had to collect sea shells from the rocks as 

 coins with which to date the formations. 



The regular succession of marine faunas in the stratified rocks 

 laid the foundation for our chronology, showed the orderl}^ develop- 

 ment of living beings, and made possible the correlation of the rocks 

 of different countries. The study of marine fossils was necessary 

 to the building uj) of historical geology on a sound basis, therefore, 

 so that the almost exclusive attention given to the seas and their 

 life was not unjustified. In those earlier days continents had a 

 place in geolog}^ mainly as limiting the migi-ations of marine faunas 

 or as providing sediments for the shallow seas. In other respects 

 they were largely negative things, vacuums where nothing took 

 place, since they provided no fossil-bearing beds, while the waters 

 around them were swarming with life and activity. 



It seemed quite the correct thing 35 years ago, when the older men 

 among us were students, to spend most of our time bending over 

 rows of brachiopods in museum cases and memorizing lists of type 

 fossils, so as to fix the age of rocks we might encounter in our field 

 work. In those days the wash of the waves and the smell of the 

 seashore seemed to permeate geology, and dry land was seldom men- 

 tioned or thought of by professors or students. Most of geology 

 consisted of stratigraphy and invertebrate paleontology. Bluff old 

 Credner has some justification for devoting nine-tenths of his his- 

 torical geology to a consideration of the doings of the sea and its 

 inhabitants. The land had scarcely been discovered. Even the 

 '"Age of Mammals" was named and subdivided in accordance with 

 the proportions of extinct to living shellfish and not from the rapid 

 evolution of the mammals and their differentiation into the highest 

 forms of animals the world has known. 



DISCOVERY OF THE LAND. 



It can not be said that the early geologists entirely ignored the 

 land. An unmistakable land surface, like the "dirt bed" of the 

 English Purbeck, with its araucarian stumps still rooted in the soil, 

 was occasionally recognized, though such occurrences are almost un- 

 known in formations older than the Carboniferous. It was recog- 

 nized, also, that heat and drought best accounted for the beds of 

 gypsum and rock salt found in several of the more ancient fomwi- 

 tions, though the materials might have come from the evaporation 

 of inclosed arms of the sea, and so might not be really continental 

 deposits. 



The most typical land deposits, those of arid and of glacial cli- 

 mates, were seldom recognized as such and were generally included 

 among the marine stratified rocks, though the absence of fossils was 



