JOINT VEINS 521 



sandstones lying in erosion channels many miles east of the eastern outcrop of the 

 parent rock ; (2) the typical basal conglomerate lying at the contact, and (3) the 

 absence of the limestones. 



Questions or remarks were made by several Fellows. 



The second paper was 



GEOLOGICAL HORIZON OF THE KANAWHA BLACK FLINT 

 BY I. C. WHITE 



Remarks on the paper were made by J. J. Stevenson, Bailey Willis, 

 and the author. The paper is printed as pages 119-126 of this volume. 



A telegram of greeting was received from A. C. Lawson, as Secretary 

 of the Cordilleran Section, and the Society by vote instructed the Secre- 

 tary to send an appropriate reply. 



The third paper was 



CORRELATION OF THE COAL MEASURES OF MARYLAND 

 BY W. B. CLARK AND G. C. MARTIN 



The paper was discussed by I. C. White, J. J. Stevenson, and Bailey 

 Willis. It is printed as pages 215-232 of this volume. 



The next paper was 



GEOLOGY OF THE POTOMAC GROUP IN THE MIDDLE ATLANTIC SLOPE 

 BY W. B. CLARK AND A. BIBBINS 



Remarks or questions were made by T. C. Hopkins, W. N. Rice', and 

 J. A. Holmes. The paper is printed as pages 187-214 of this volume. 

 An abstract is printed in Science, volume xv, page 84, January 17, 1902, 

 under a different title. 



The following paper was then read : 



JOINT VEINS 

 BY G. K. GILBERT 



[A bstraci] 



Certain thin beds Of limestone inclosed in Cambrian shales of Rainbow valley, 

 House range, Utah, are traversed by systems of parallel veins. These veins repre- 

 sent joints and afford a convenient opportunity for the study of joint arrangement. 

 The intervals between parallel joints are so small that many characters, including 

 the interrelations of systems, are well exhibited in hand specimens. It is sug- 

 gested that the scale of joint systems is in part determined by the thickness of the 

 formation traversed. At least twelve systems occur in one specimen. Some of 



