The Two Islands. 31 



by another. A friendly geological student 

 found in Northern California a Triassic shell, 

 the Halobia, recognized as of determining 

 importance, while the same season a surveyor 

 brought more of these shells from the region 

 of Wallowa lake, plainly Halobia, too, thus 

 proving the twin character of the two islands 

 of our story. 



These facts readily suggest a nucleus for 

 each island in the Triassic period, an exten- 

 sion of these in the Jurassic and a continuous 

 envelopment of both regions throughout the 

 Cretaceous; for the Trigonia, a bivalve shell 

 of Cretaceous times, is abundant in both re- 

 gions, and of the three or four species most 

 abundant on the coast all are common in the 

 fossil beaches of both islands. Two species 

 of Trigonia may be seen on Plate II. 



A handsome marine gastropod, allied in 

 form to Actionella and Acteonina of this same 

 period, and closely resembling the land shell 

 Bulimus, is found abundant in the rock of 

 both regions. 



