722 



SCIENCE. 



[N. S. Vol. II. No. 48. 



The formations range in age from Algon- 

 kian to Cretaceous, the greater portion be- 

 ing Algonkian, Cambrian and Silurian. 

 The Silurian rocks appear in the Shenandoah 

 Valley, the Cambrian in Catoctin Moun- 

 tain and Blue Ridge, the Algonkian between 

 these ridges, and the Jaratrias east of 

 Catoctin. The Algonkian rocks are chiefly 

 granite and epidotic schist ; the Cambrian 

 rocks, sandstones and shales, passing up 

 into limestones ; the Silurian rocks, lime- 

 stones and shales ; and the Juratrias rocks, 

 red sandstone and shale and limestone con- 

 glomerate. The details of the strata are 

 shown in the columnar section. The man- 

 ner in which each kind of rock decays is 

 discussed, and how the residual soils and 

 forms of surface depend on the nature of 

 the underlying rock. 



In the discussion of Structure, after a 

 general statement of the broader structural 

 features of the province, three methods are 

 shown in which the rocks have been de- 

 formed. Of these the extreme Appalachian 

 folding is the chief ; next is that developed 

 in the Juratrias rocks, and least in impor- 

 tance are the broad vertical uplifts. Three 

 degrees of extreme deformation appear in 

 the Paleozoic rocks^ — folding, faulting and 

 metamorphism — each being best developed 

 in a certain kind of strata. Between Blue 

 Ridge and Catoctin Mountain the Algon- 

 kian or oldest rocks appear on a great anti- 

 clinal uplift, with Cambrian rocks on either 

 side. Faults appear chiefly on the west 

 side of this uplift, and metamoi'phism in- 

 creases toward its east side. In the Shenan- 

 doah Valley the rocks are folded to an ex- 

 treme degree, and the strata are frequently 

 horizontal or overturned. The Juratrias 

 rocks always dip toward the west, and are 

 probably repeated by faults different in 

 nature from the Appalachian faults. In 

 the sheet of sections the details of the folds 

 and faults appear. 



Economic products of this region com- 



prise copper and iron ore; ornamental 

 stones, such as marble, limestone conglom- 

 erate and amygdaloid; building stones, such 

 as sandstone, limestone and slate; and other 

 materials like lime, cement, brick clay and 

 road materials. The localities of each of 

 these materials are noted and quarries 

 located on the economic sheet, and the char- 

 acter and availability of the deposits are 

 discussed. 



AMERICAN FOSSIL BBACHIOPODA. 



The writer has had in preparation since 

 1886 'A Synopsis of American Fossil Brachi- 

 opoda, including Bibliography and Synon- 

 ymy.' This work, now completed, will ap- 

 pear as one of the Bulletins of the U. S. Na- 

 tional Museum and embraces the following 

 chapters: I. Geological Development ; II. 

 Brachiopod Terminology; III. Biological 

 Development; IV. Morphology of the Bra- 

 chia, by Charles E. Beecher ; V. Classifica- 

 tion; and VI. Index and Bibliography. 

 The following summary, taken from this 

 work, gives some of the more important re- 

 sults obtained, all of which are discussed at 

 length in the work above cited. 



In North America there are one thou- 

 sand eight hundred and forty-six Paleozoic, 

 thirty-seven Mesozoic, and nine Cenozoic 

 species of fossil lirachiopoda. There are 

 one hundred and one species in the Cam- 

 brian, three hundred and eleven in the Or- 

 dovician, three hundred and twenty in the 

 Silurian, six hundred and fifty^five in the 

 Devonian, and four hundred and eighty- two 

 in the Carboniferous. 



This remarkable scarcitj^ of Post-Paleo- 

 zoic species in America is supposed to be 

 due not so much to the general decline of 

 of the class as to great orographic move- 

 ments during the close of the Paleozoic, 

 thus producing complete barriers against 

 the introduction of species from other areas. 

 Moreover, few marine sediments are found 

 in them. 



