BUFFALO SOCIETY OF NATURAL SCIENCES 109 



lime shows under the microscope an exceedingly fine-grained lime 

 mud, the grains being angular and of varying sizes, with rhombic 

 crystals of dolomite scattered through the mass of calcite fragments. 

 There are also many fine, black specks, probably of carbonaceous 

 material. The most significant fact of the composition, however, is 

 the presence of the silica and the alumina, which forms nearly one- 

 third of the rock. Such a composition is entirely incompatible with 

 the idea of chemical deposition, where we should expect practically 

 pure carbonates. 



(b and c) Organic origin. If the Bertie were an organic deposit 

 its fine texture would permit of only two types of organisms active in 

 its formation, namely, the protozoa or the algae. The lime content 

 might be supplied by Foraminifera or by lime-secreting algae, the 

 silica by Radiolaria. The microslide of the Bertie shows no trace 

 of any of these organisms. One other method of organic deposition 

 is possible. The work of Drew, Sanford, and Vaughan has recently 

 shown that in warm or tropical seas certain bacteria are active in 

 precipitating calcareous muds from the sea water. That the Bertie 

 water! ime could not have had such an origin is evident from its 

 chemical composition given on page 106 above, in which the silica 

 and alumina play too important a part, amounting to 28.98 per cent 

 of the whole. 



Since the chemical and microscopic study of the Bertie proves the 

 impossibility of either a chemical or an organic origin, we must con- 

 clude that the rock is clastic. 



(d) Clastic origin. A rock of clastic origin may have one of two 

 sources: (V) it may be composed of material which was originally 

 derived from the sea, that is, it may be thalassigenous, or (2') it may 

 be derived from the erosion or breaking up of a pre-existing rock on 

 the land, that is, it may be of terrigenous origin. 



(V) Organic materia] broken up in the sea by organisms, or along 

 the shore by waves, consists of shells, corals, and other hard parts of 

 organisms mixed with varying amounts of sands and muds, organic 

 and inorganic, the composition depending on the character of the 

 rock supplying the detritus. Such clastic deposits are especially 

 well developed around coral reefs where the purely biogenic rocks 

 grade laterally in all directions into the clastic ones. That the Bertie 

 waterlime could not have been a lime mud derived from the erosion 

 of coral or other reefs and deposited in the surrounding quieter water 

 or in the lagoons, as in the case of the similar, fine-grained lime mud 



