124 



SCIENCE 



[N. S. Vol. XXX. No. 760 



Most of the specimens obtained were kindly 

 identified for me by Dr. Stejneger, of the 

 U. S. National Museum. 



H. A. Allaed 

 BuEEAu OF Plant Industry, 

 Washington, D. C. 



SOCIETIES AND ACADEMIES 



THE QEOLOQICAL SOCIETY OF WASHINGTON 



The 220th meeting of the society was held at 

 the Cosmos Club on Wednesday evening, May 12. 



Regular Program 

 Significant Time-breaks in Goal Deposition: Mr. 



Geo. H. Ashley. 



In a study of the results which were recently 

 published in Economic Geology, it was found that 

 one foot of bituminous coal, if deposited under 

 present-day conditions, would require at least 

 three hundred years for its laying down. 



Considering the known variation in the thick- 

 ness of single coal beds, the question arises as to 

 whether it may not prove possible to use a coal 

 bed as a measuring rod for the time of deposition 

 of other beds in the coal measures. Thus, in the 

 case of a bed 15 feet thick in one district and 18 

 inches in another, if the coal in each case were 

 deposited at the same rate, the 15-foot bed re- 

 quired at least four thousand years longer than 

 the 18-inch bed. Study was made to see if where 

 the coal was thin there was a compensating thick- 

 ening of the adjoining rocks. As far as the study 

 was carried no such compensating thickening could 

 be found. It was therefore assumed that in the 

 eases examined the thin bed of coal represents 

 approximately all of the deposit made at that 

 point during the time required for the deposition 

 of the thick bed near by. This resulted from 

 either slow growth or time-breaks either in or 

 just preceding or following the thin coal bed 

 itself. 



A study of the rate of deposition of certain 

 peats in Europe leads to the conviction that in 

 many cases the difference in thickness is due to 

 difference in rate of deposition, while in other 

 cases the difference would seem to be due to time- 

 breaks or periods of non-deposition. 



The evidence of these time-breaks may consist 

 of " smooth partings," which, as in the Lower 

 Block coal of Indiana, may locally show as un- 

 conformities between the under- and overlying 

 beds, or of smooth partings which are represented 

 in other districts by up to 40 feet of shale and 



sandstone, as in Coal IV. of Indiana. In other 

 cases one or two inches of cannel coal or bone 

 may be represented in an adjoining district by a 

 thick parting, as in the Moshannon bed, west of 

 Houtzdale. In some beds partings of clay, shale 

 or sandstone, where they are known, are uni- 

 formly thin and regular. In other beds they will 

 vary from one fourth inch up to 40 or 50 feet. 

 In such cases the great thickness of the parting 

 often suggests, even though it does not prove, a 

 considerable time interval. 



A study of the problem seems to indicate clearly 

 that the elements of slow growth and of tem- 

 porary non-deposition can not be eliminated from 

 it, and that it would be scarcely right to say that 

 the rocks forming a parting in the coal, or that 

 a certain thickness of rocks above or below the 

 coal, may have taken a certain number of years 

 for their deposition, equivalent to the time repre- 

 sented by the difference in the thickness of the 

 coal at that point and at the point of greatest 

 thickness, multiplied by an assumed rate of depo- 

 sition of the coal. 



Cretaceous Geology of the Carolitias and Georgia: 

 L. W. Stephenson. 



The belt of Cretaceous deposits which, with 

 certain interruptions, extends along the inner 

 margin of the coastal plain from Marthas Vine- 

 yard, Mass., to Cairo, 111., has its widest areal 

 development in the region of southeastern North 

 Carolina and northeastern South Carolina. 



In North Carolina three Cretaceous divisions 

 are recognized. The oldest of these is of lower 

 Cretaceous age, and consists of about 275 feet of 

 light-colored, coarse, generally compact or par- 

 tially indurated, feldspathie, cross-bedded sands 

 with inter-stratified lenses of massive more or 

 less sandy clays. So far as known these materials 

 are non-fossiliferous. The beds are separated 

 from the overlying Cretaceous strata by an un- 

 conformity. Employing physical criteria, the divi- 

 sion has been correlated approximately with the 

 Patuxent formation of Virginia and Maryland. 

 The name Cape Fear formation was proposed for 

 this terrane by the writer in a paper entitled 

 " Some Facts Relating to the Mesozoic Deposits 

 of the Coastal Plain of North Carolina," which 

 appeared in 1907. 



The next younger division, which is of upper 

 Cretaceous age, consists of 500 to 600 feet of dark 

 to black lignitic, irregularly bedded and for the 

 most part laminated, sands and clays, with inter- 

 bedded marine lenses in the upper portion. As 

 regards their structural relations the beds rest 



