Hershey.] 



Isthmus of Panama. 



239 



Franciscan series in California, but the occurrence appears to be 

 different except that in a few cases the latter also have been invaded 

 by and are enclosed in eruptives. 



The age of this igneous complex will be discussed after the 

 succeeding formation has been described. 



TIic Torio Limestone. — The next formation seen in going up the 

 coast from the Torio River is a hard, light gray, massive limestone. 

 It is sometimes nearly pure and is then sub-crystalline. More 

 often it is very impure but its outcrop always reveals its calcareous 

 character. In places it abounds in fossils (mostly shells of marine 

 brachiapod or lamellibranchiate species) which are so cemented 

 into the rock that they can not be separated from it. In a few 

 places the rock is a regular breccia-conglomerate of fossils and rock 

 fragments from older formations, including the green igneous rock. 

 Like the preceding formation, it is exceedingly well supplied with 

 irregular veinlets of white quartz and calcite, which are not common 

 in any succeeding formation. It is impossible to tell the thickness 

 of the limestone, but it is at least several hundred feet. The strike 

 of the formations along this coast is generally parallel to the beach, 

 and hence it is difficult and often impossible to determine their 

 thickness. 



Limestone is exposed along the coast at low tide in several 

 small irregular patches. In the case of the most southerly ones it 

 is surrounded by and appears to overlie the igneous massif. At 

 several places it is exposed very close to the latter and contains 

 strata of conglomerate which dip away from the contact and which 

 contain fragments of the green igneous rock; hence, it is evidently 

 newer than the latter. 



This limestone is well exposed on the Torio River, a few miles 

 from the coast, in many irregular patches of light gray limestone, 

 some of which are of small extent and others quite important. 

 It is here always well stratified, being moderately thin-bedded and 

 dipping steeply in one or another direction. It clearly overlies the 

 green igneous formation, but along the contact is much contorted, 

 and masses of dark gray diorite of fine grain but distinct holocrys- 

 talline structure, have been injected into the limestone. 



The green igneous rock and the limestone are closely related in 



