170 TRANSACTIONS OF THE [FEB. 15, 



bog holes. Away beyond this divide I could just distinguish a 

 dim outline over toward the Magdalena river, and if there should 

 be only a little depression at the divide, a part of this river 

 would come, flooding all the valle}^ of the Rancheria. I saw 

 many indications that this had once been the case, and that in 

 earlier times, before the valle3's were filled up, all the lowlands on 

 which I was looking had been a great embay nient with the Sierra 

 Nevada mountains and island lying well off the shore, and the 

 mouth of the Magdalena river, farther back among the moun- 

 tains, with the flat lands and swamps gradually forming around 

 it. The whole structure of the valley seemed to indicate such 

 developments. Alluvium growing deeper as one proceeded in- 

 land, marls and fossils. toward the sea, the even surface of the 

 valley, its general outline and slight elevations, while the float 

 rock containing fossils similar to those well above the sources 

 of the present rivers, was very suggestive 



Material brought down b3' the Magdalena river might easily 

 be considered sutticient to form silt deposits that would gradu- 

 ally make a series of swamps and lagoons where vegetable ma- 

 terial could have accumulated, to be later covered by the residue 

 from floods which would make the conditions necessary to car- 

 bonize such accumulated masses. 



Fossils that were perhaps of late Cretaceous age were found 

 in place on a denuded limestone lying on the surface of the 

 valley toward the Sierra Nevada mountains, and northeast of 

 the Cerrajon Peak. This indicated that salt water had once ex- 

 tended thus far, and the alluvium and float rock gave evidence 

 of a gradual encroachment of material brought down the valley 

 by some agency which must have been much greater and more 

 extensive than the present rivers. I looked a long time, imagin- 

 ing one thing or another till at last my guide warned me that it 

 was getting late. 



Next morning after the ascent of the mountain, we tried to 

 work at the ledge of vock by the Cerrajon river, but were sa 

 hindered by the water that after three days we gave up all 

 thought of further digging. The coal found was nearlj' like that 

 in other places. 



During the next week I examined all the valley to the divide 

 west along the southern base of the Sierra Nevadas and on ta 

 the main channel of the Cesar. I found abundant outcroppings 

 of coal continuous along the base of the Black Andes till the 

 clay and the shale deposits of the valley were lost under a su- 

 perficial stratum of alluvium. Along the base of the Sierra 

 Nevada mountains I noted numerous great boulders of red and 

 white conglomerate and the older crystalline types, granite^ 



