PALEOZOIC GROUP. 305 



strata, is not easy to explain from the study of them alone; but the excessive 

 Post- Silurian dynamism is abundantly manifested wherever a view of the 

 subjacent rocks can be had. 



The fossils of the Deep Creek division are extremely numerous in some 

 localities and almost abesent from others. The nodules referred to in No. 2 

 of the section suggest an organic origin more by their form than by their 

 texture or markings, although there is the semblance of pores upon the sur- 

 face occasionally. The Stromatopora? beds and some of the associated strata 

 coutain enormous quantities of a peculiar marking which needs more study 

 than has yet been possible. They seem to belong among the sponges, al- 

 though this opinion may not be taken as authoritative at present. Some of 

 the strata of a different character are almost certainly sponges, but the writer 

 has not had opportunity to study them thoroughly. Associated with these 

 are forms not the best for determining doubtful paleontological questions, as 

 they are largely the internal casts of G-asteropods. Straparollus sanctisabce, 

 Rcem. (sp.). a smaller Straparollus, Platyostomaf, Holopea (sp. ind.), and a 

 doubtful Helicotoma, with what appear to be Annelid borings, are abundant 

 in the "spongy chert." In lower strata several Orthoceratites are common. 

 I am unable from lack of literature to determine these accurately, but one 

 resembles Orthoceras imbricatum, Sowerby; another is near 0. multicamera- 

 tum, Emmons; and a third may perhaps be an undescribed form. This last 

 is short conical, with septa in number between the other species named, and 

 the siphuncle is eccentric, narrowing conically from the body cavity back- 

 ward. If it prove to be new I propose the name Orthoceras sansabensis. 



TAXONOMY OF THE SYSTEM. 



The classification of the Silurian terranes as arranged in the preceding 

 pages is not wholly satisfactory, although it is the best tentative scheme 

 which can now be framed. In any use which may be made of it, our present 

 inability to explain the exact relations of the Post-Hoover divisions should 

 be borne in mind. There is at least a little suspicion that a part or all of the 

 San Saba Series may be entitled to rank as a separate (JNTiagaran) system. 

 Here is another unsolved problem which we go afield to study in 1890. The 

 schedule below recapitulates what has already been given in detail. 



