786 



SCIENCE. 



[N. S. Vol. III. No. 73. 



reasons are given (based on the study of the 

 faunas themselves) for thinking the Chouteau 

 was later than the Chemung. From a similar 

 stvidy, the author concludes that there is not at 

 hand suiiicient evidence of the composite origin 

 of the fauna in question. 



North American Graptolites : By E. E. Gueley. 

 The present paper is a continuation of one 

 in the January-February number of the Journal. 

 The vertical range of graptolites is quite fully 

 discussed and tables are given showing the hori- 

 zon and geological range of each species so far 

 as the facts are known. The value of these 

 tables is much enhanced by references to the 

 original sources of information in a large num- 

 ber of cases. The author finds that graptolites 

 may be clearly traced to the beginning of the 

 Carboniferous period, and he thinks it likely 

 that allied genera lived through the Paleozoic. 



Deformation of Socks, II., An Analysis of Folds: 



By C. R. Van Hise. 



Folds are divided into simple, composite and 

 complex. The author compares a rock fold to 

 a wave of the sea, each large wave having super- 

 posed on it waves of the second order, these 

 having waves of the third order, etc. Thus 

 while the forces producing them are different, 

 the complexity of the two are comparable. 

 Various forms of folds are figured, and the rela- 

 tion between them clearly stated. Simple 

 folds may be united to produce a great variety 

 of composite structures, anticlinoria and syn- 

 clinoria. These may be normal or abnormal 

 and upright, inclined or overturned. As to 

 abnormal composite folds, several factors modify 

 the result. (1) Readjustment between the 

 beds; (2) the great strength of the older rocks; 

 (3) decreasing lateral stress with depth ; (4) the 

 position of the fold in the group of rocks folded. 

 Complex folds are folds considered in three di- 

 mensions. This complexity may be due to dif- 

 ferences in thickness and strength of beds in 

 different places, unequal thrust on different 

 parts of the border of an area, and to the fact 

 that thrust may be in two or more directions. 

 A number of practical directions are given for 

 discovering and interpreting in the field the 

 structure of complex folds. 



C. R. Van Hise continues the ' Summary of 



Current Pre-Cambrian North American Litera- 

 ture.' S. Weller contributes a review of Wil- 

 liams' 'Geological Biology.' A long list of the 

 publications recently received closes the number. 



D. P. N. 



SOCIETIES AND ACADEMIES. 



GEOLOGICAL CONFERENCE OF HAKVAED UNIVER- 

 SITY, APRIL 28, 1896. 

 (1) April recess excursion to the Middle Susque- 

 hanna, Pa : By W. M. Davis. 

 The special object of this excursion was to 

 study on the ground the deflected tributaries of 

 the Susquehanna in Union and Snyder counties. 

 Pa. , and to determine their bearing on the hy- 

 pothesis that the Susquehanna was superposed 

 by flood plaining on the two synclines of Pocono 

 sandstone in Dauphin county at a late stage in 

 the Cretaceous cycle of denudation. (See Rivers 

 and Valleys of Penna., Nat. Geogr. Mag., I, 

 1889, 241.) Spruce run and Buffalo creek, 

 Penn's creek and Middle creek were examined ; 

 Penn's creek being the most significent, as it 

 abandons a well-defined limestone and shale 

 valley and turns south through ridges that sur- 

 mount by a moderate measure the Tertiary 

 peneplain of the region. These various streams 

 cannot be regarded as antecedent to the time 

 of mountain folding, for they are systematically 

 placed with respect to the Susquehanna ; they 

 cannot be regarded as adjusted to the structures 

 of the region, for they stand in most diverse 

 relation to resistant and weak strata and to an- 

 ticlines and synclines ; their systematic south- 

 ward deflection suggests the influence of an 

 ancient flood plain of the Susquehanna that was 

 formed on a peneplain of the past, of just the 

 same kind as the influence exerted by the grow- 

 ing flood plain of to-day at Selin's Grove, where 

 Penn's creek, after approaching within half a 

 mile of the main river, has to flow four miles 

 southward along the inner border of the plain be- 

 fore mouthing. Admitting that the deflection of 

 the several streams was caused by flood plaining, 

 this is shown to have been ancient, not only by 

 the relation of Penn's creek to the low ridges 

 that surmount the dissected Tertiary peneplain, 

 but also by the imminent readjustment of some 

 of the deflected streams by longitudinal subse- 

 quent streams that are growing along weak 



