8 MICROSCOPICAL EXAMINATIONS 



a truly wonderful development of minute organic forms, consisting chiefly of 

 Polythalamia, which occur in an abundance rivalling those vast accumulations 

 of analogous forms constituting the marls under the city of Charleston, S. C. 



2d. While there is a general resemblance between the species found in all 

 the deep soundings above mentioned, the same species of Polythalamia occurring 

 with few exceptions at each locahty, yet each place has its predominant species ; 

 thus in the most southerly sounding, (H,No. 1, 90 fathoms,) there occui's a much 

 greater number of Globigerina than in any of the others ; while Textilaria atlan- 

 tica, although present, is by no means so abundant as in '••G, No. 8, 89 fathoms." 



3d. Infusoria, as well as Polythalamia, occur in the deep soundings ; but the 

 infusoria are few in number, and consist of Coscinodisci, Gallionella sulcata, 

 and other species, which probably swim freely in the ocean ; while none of the 

 littoral parasitic species, such as Achnanthes, Isthmia, Biddulphia, Striatella, 

 and Synedra are found. 



4th. It is worthy of notice that in the deep soundings not a single specimen 

 was found of Polythalamia belonging to the Plicatilia of Ehrenberg, (Agathisti- 

 ques of D'Orbigny,) while a number of these forms were found in the sliallow 

 soundings, and they are well known to occur in vast quantities around the shores 

 of Florida and the West India Islands. This group of Polythalamia appears 

 to have been created after the deposition of the chalk formation, in which no 

 trace of such forms occur, while they are very abundant in the tertiary deposites. 

 Their entire absence in the deep soundings, where vast numbers of other Poly- 

 thalamia occur, and their presence in littoral deposits, would seem to indicate 

 that for their abundant development comparatively shallow seas are necessary ; 

 thus affording additional evidence of dift'erence in the depths of the seas from 

 which the cretaceous and tertiary beds were deposited. 



5th. The deep soundings were all from locahties which are more or less un- 

 der the influence of the Gulf stream, and it is not improbable that the high tem- 

 perature of the waters along the oceanic current may be cause of immense 

 development oforganic life, making its path, as is shown by the soundings, a per- 

 fect milky way of Polythalamia forms. The deposits under Charleston may have 

 been produced under the similar influence of an ancient gulf stream. 



6th. From the presence of such great numbers of Polythalamia in the deep 

 soundings, there results a very large proportion of calcareous matter, thus pre- 

 senting a striking diflference between them and the quartzose and felspathic 

 sands nearer shore. 



7th. The littoral sands obtained in shallow soundings at first view appear to 

 afford little promise of affording any Infusoria. But notwithstanding their coarse, 

 and, in some cases, even gravelly nature, they all yield by levigation a consider- 

 able number of silicious Infusoria, which in variety and abundance exceed those 

 found in the deep soundings. 



8. None of the soundings present anything resembling the vast accumulations 

 of Infusoria which occur in the Meiocene infusorial marls of Virginia and Mary- 

 land ; and, indeed, I have never found, even in estuaries, any recent deposit at 



