chap. xii. Port S. Julian. 375 



teen Polygastrica and twelve Phytolitharia. Of these 

 organisms, seven are new forms, the others being pre- 

 viously known : all are of marine, and chiefly of oceanic, 

 origin. This deposit to the naked eye resembles the 

 crust which often appears on weathered surfaces of 

 feldspathic rocks ; it likewise resembles those beds of 

 earthy feldspathic matter, sometimes interstratified with 

 porphyritic rocks, as is the case in this very district 

 with the underlying purple claystone porphyry. From 

 examining specimens under a common microscope, and 

 comparing them with other specimens undoubtedly of 

 volcanic origin, I had come to the same conclusion with 

 Prof. Ehrenberg, namely, that this great deposit, in its 

 first origin, is of volcanic nature. 



Tort 8. Julian. — On the south side of the harbour, 

 the following section, which I here repeat, gives the 

 nature of the beds seen in the cliffs of the ninety feet 



* No. 33. 



Section of the strata exhibited in the cliffs of the 90-feet plain, at Port 

 S. Julian. 



«^*<* -^» --jvs-^f-rj . — '-*<v .. ^.-v^,^ <-•- .- . &,t-o cd ■ — » m. ex- 



plain. Beginning at the top, — 1st, the earthy mass 

 (A A), including the remains of the Macrauchenia, with 

 recent shells on the surface; 2nd, the porphyritic 

 shingle (B), which in its lower part is interstratified 

 (owing, I believe, to redeposition during denudation) 

 with the white pumiceous mudstone ; 3rd, this white 

 mudstone, about twenty feet in thickness, and divided 

 into two varieties (C and D), both closely resembling 

 the lower, fine-graiDed, more unctuous and compact 

 kind at Port Desire ; and, as at that place, including 

 much selenite ; 4th, a fossiliferous mass, divided into 



