128 PATAGONIAN EXPEDITIONS! NARRATIVE. 



valley of the gap through which we had passed. As just stated, we found 

 these to belong to the Patagonian formation. They were chiefly sand- 

 stones and were inclined at a high angle to the eastward. They were rich 

 in the remains of marine invertebrates. A species of oyster, Ostrea ingens, 

 common to that formation, was especially abundant and of exceptional size 

 even for that unusually large form. Frequent examples were observed in 

 which a single valve would measure a foot in length and the combined 

 weight of a single specimen, including both upper and lower valves, could 

 scarcely have fallen much, if any, short of forty pounds. 



After resting and grazing our horses for an hour or two at this place, 

 which we christened Shell Gap, we proceeded a few miles farther to a 

 thicket of small beech trees or bushes growing at the foot of a low hill, 

 some three or four hundred yards beyond where the stream flows through 

 a rugged canon, cut in the southern walls of the great valley which we 

 named Mayer Basin. Here, convenient to a spring of splendid water 

 with an abundance of grass for our horses and firewood sufficient for our 

 purpose, we proceeded to establish a permanent camp in a well sheltered 

 place, where we might spend a number of days in making collections repre- 

 sentative of the surrounding flora and fauna and in studying the geology 

 and geography of the vicinity. Hardly had we pitched our tent, put things 

 to rights and set a few dozen traps in apparently advantageous places, 

 when a cold drizzling rain set in and continued throughout the night. 



