11. Authorities carried out 1, 200 controlled blasts to dig through the tough rock structure . 12. The rock structure was created during the Alpine orogeny and exposed by subsequent erosion. 13. The preglacial drainage pattern was controlled by the rock structure . 14. He was first attracted by the general rock structure of the Rouyn area in 1911. 15. It was listed in a group with many other lava rock structures in Lincoln counties. 16. A knowledge of the underlying rock structure helps to predict the location of mineral deposits. 17. A driver was washing his carriage on the point when the rock structure gave way. 18. Few men have equalled him in the truthful rendering of rock structure and mountain form. 19. Soft ground or mixed tunneling was used where there was insufficient rock structure for underground support. 20. After the small building was rebuilt, the rock structure was used almost entirely as a church.
