66 EARTH FEATURES AND THEIR MEANING 



ture structures are for this reason much more likely to be over- 

 looked, and if they are not to elude the observer, they must be 

 sought out with care. Fold and fracture structures may both be 

 revealed upon the same map. 



READING REFERENCES TO CHAPTER VI 



Joint systems : 



JOHN PHILLIPS. Observations made in the Neighborhood of Ferrybridge 

 in the Years 1826-1828, Phil. Mag., 2d ser., vol. 4, 1828, pp. 401-409 ; 

 Illustrations of the geology of Yorkshire, Pt. II, The Limestone Dis- 

 trict. London, 1836, pp. 90-98. 



SAMUEL HAUGHTON. On the Physical Structure of the Old Red Sand- 

 stone of the County of Waterford, considered with reference to cleav- 

 age, joint surfaces, and faults, Trans. Roy. Soc. London, vol. 148, 

 1858, pp. 333-348. 



W. C. BROGGER. Spaltenverwerfungen in der Gegend Langesund-Skien, 

 Nyt Magazin for Naturvidernskaberne, vol. 28, 1884, pp. 253^19. 



WM. H. HOBBS. The Newark System of the Pomperaug Valley, Con- 

 necticut, 21st Ann. Rept. U. S. Geol. Surv., Pt. Ill, 1901, pp. 85-143. 



Geological map : 



WM. H. HOBBS. The Interpretation of Geological Maps, School Science 

 and Mathematics, vol. 9, 1909, pp. 644-653. 



