LKWIS, OX DIATOMACE.E. 157 



• 



orgaiiisms, -without reference to the kind and manner of life 

 they once invested. 



As an additional argument in favour of the study of 

 living species, it may here be mentioned that many 

 of the fossil forms are still to be found as living species 

 on the coast, or under circumstances which prove them 

 to have been alive at no very remote period. It is not 

 unusual to meet with some of these in the Delaware tidal 

 mud, and a still larger number are to be found in the 

 blue clay — (old estuary) deposit immediately underlying it. 

 Among these a few of the most common are Eupodiscus 

 Ralfsii,E.argus, Coscinodiscus gigas, C. ocul-iridis,C. centralis, 

 Triceratium striolatum, T. punctatum, Actiniscus sirius, &c. ; 

 Sceptroneis caduceus occurs living on algse at Riviere du Loup, 

 St. Lawrence River, Goniothecium obtusum at Black Rock 

 Harbour, L. I. 



The important question, too, of the influence of locality on 

 the growth and development of species nowhere presents 

 itself in so interesting a point of view as in this country. 

 The large extent of its sea board, embracing every variety of 

 climate, the continuous chains of estuaries and sounds along 

 the entire line of coast, and the many rivers, large and small, 

 traversing every kind of soil from the southern alluvial to the 

 granite ranges of the north-east, offer an unsurpassed field for 

 the study of this influence. 



Although not able to pursue the subject at this time, I 

 cannot refrain from alluding to a fact whicii forces itself on 

 the mind at an early stage of these investigations, viz., the 

 great distance from the sea at which marine influences con- 

 tinue to make themselves felt. Philadelphia is situated 

 nearly a hundred miles from the ocean, and even at the period 

 of spring tides at least fifteen miles above the faintest suspi- 

 cion of brackish water, and yet quite a number of the diatoms 

 in the Delaware at this point are purely marine, and a still 

 larger number brackish. The agency of migratory fish, 

 as the shad and low-swimming sturgeon, in bringing about 

 this result, is no doubt important, but will not serve to 

 explain the presence of brackish and marine species in the 

 ditches adjoining Cooper's Creek, a tributary of the Delaware, 

 and in Fox Chase Run, some ten miles above this city, at 

 points not within tidal range. The old estuary bed of the 

 Delaware, (blue clay) before alluded to, was very rich in these 

 forms, and by digging down a short distance at any part of 

 the meadow land bordering the river the blue clay which 

 contains them may be exposed. An idea which naturally sug- 

 gests itself under these circumstances as a solution of this para- 



