692 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



Smith devoted many years to the tracing of surface outcrops of different layers 

 of slightly tilted strata across a part of England and collected and kept separate 

 the fossils from each stratum. He recognized that each stratigraphic unit was 

 characterized by a set of genera and species and that these faunas differed one 

 from the other in the succession of beds from the base to top. He found that a 

 single stratum when followed for long distances along the surface contained the 

 same assemblage of species and that any particular isolated layer of rock could 

 be identified by the fossils within it as belonging to a certain bed within a suc- 

 cession of strata. The trends of each stratigraphic member were drawn in color 

 on maps with sections showing the sequence of layers as they passed beneath 

 the surface. These maps, published with an explanatory text (W. Smith, 1815), 

 constitute the first large areal geologic map. It served as the foundation of a 

 new epoch for the presentation of the results of field work and stratigraphic 

 research to the scientific public, and opened a wealth of accurate information 

 to the geologists of the Continent who were concerned with unraveling the geo- 

 logic history of Mesozoic rocks. 



Conybeare and Phillips (1822), following the principles set forth by Smith, 

 published the results of their investigations in England and Wales and classi- 

 fied strata ranging in age from middle Paleozoic to Eecent. The terms Eocene, 

 Miocene, and Pliocene later introduced by Charles Lyell were not employed but 

 rocks corresponding to these ages were recognized and referred to according to 

 their mineral composition. The Cretaceous was divided into upper and lower 

 units and the Jurassic into the Oolitic system and the Lias, the former being 

 subdivided into upper, middle, and lower Oolite. The New Red Sandstone be- 

 neath the Oolitic was placed in the lower Mesozoic and above a fourfold division 

 of the Carboniferous, the upper part of which was considered as equivalent to 

 the Zechstein of Germany. The Old Red Sandstone was included within the 

 Carboniferous until later assigned to the Devonian by Sedgwick and Murchison. 

 The lower Mesozoic in Germany was studied in detail by various workers and 

 divided into three members with the Bunter sandstone at the base, the ]\Iuschel- 

 kalk limestone in the middle, and the Keuper at the top; in 1834 the name Tri- 

 assic was applied to the group by Alberti. The absence of the marine middle 

 member in Great Britain was early recognized by British geologists. 



In England, below the Old Red Standstone and above the granites and 

 crystalline schists are a series of slates, limestones, and indurated sandstones 

 which have suffered intense deformation. These rocks were studied by Sedgwick 

 and Murchison and ultimately classified as the Cambrian and Silurian systems. 

 The scarcity of fossils and the complexity of the stratigraphy rendered it im- 

 possible at first to establish the boundary betw^een the two systems, with Murchi- 

 son and Sedgwick becoming bitter enemies over the Cambrian. Murchison later 

 (1839) included the entire assemblage of strata in the Upper and Lower Silu- 

 rian and considered Sedgwick's Cambrian as a part of the Lower Silurian. Ulti- 

 mately, however, Sedgwick's Cambrian was shown to be distinct from the 

 Silurian. In 1879 the Lower Silurian rocks were studied by Lapworth and placed 

 in a new system which he named the Ordovician. Meanwhile the Continental 

 geologists examined the middle Paleozoic rocks in Germany, Belgium, Austria, 

 and Scandinavia and attempted to make correlations with the succession of 

 strata established in Great Britain bv Sedgwick and Murchison. Among the 



