1907.] THOMSON— PROGRESS OF THE ISTHMIAN CANAL. 131 



Within the Culebra cut the highest point of the divide is now 

 about 167 feet above sea level, having been originally or before any 

 cut was made about 333 feet. The French cut down 160 feet. At 

 this point the additional cutting required to complete the canal is 

 about 127 feet. A total depth of cut of about 290 feet will thus 

 be needed. A sea level canal would have made this 375 feet. 

 Naturally the amount of earth to be removed increases with the 

 depth because the greater depth requires much wider cutting to 

 provide reasonable slopes safe from landslips, and the length of 

 the excavation is likewise greatly extended. The money expendi- 

 ture for the sea level project as well as the time needed would have 

 been several fold more than for the lock or present plan. 



Explosives are used both in the rock at Obispo and in the compact 

 earth at Culebra and in January last, it is reported, about eleven 

 miles in total length of holes were drilled for blasting. Beyond 

 Culebra the site of the first lock on the Pacific side, which is known 

 as the Pedro Miguel lock, was soon reached. It is to be a duplicate 

 lock with a single drop from the 85-foot level, of about thirty feet 

 or a little less. 



At its foot another fresh-water lake at 55 feet above sea-level 

 will be made by dams at a place called La Boca, about two miles 

 from the city of Panama and to the west thereof. The area of 

 this lake will be upwards of ten square miles. Alongside of the 

 La Boca dam will be located the Sosa locks at Sosa hill. These 

 will be in duplicate and in a flight of two with level differences of 

 about 2y feet or more, or 55 feet for the two locks. Inasmuch, how- 

 ever, as the maximum tides at Panama are as great as 24 feet, pro- 

 vision for variation in the lock levels is made in accordance there- 

 with. At Colon the tides are a little more than 2 feet. From the 

 foot of these locks at Sosa a channel is to be dredged straight out 

 to sea in the Bay of Panama, the locks at Gatun being similarly 

 reached from the Atlantic side by a straight channel out to sea in 

 Limon Bay, upon which bay Colon is situated. Practically none 

 of this work of dredging is yet done. 



Since the present plans follow a different route from that adopted 

 by the French, the dredging accomplished by them in not now of 

 use. The city of Panama is about two miles to the east of the 



