G. M. DAWSON — GEOLOGY OF MIDDLETOK ISLAM). 429 



till, of rather dark, bluish-gray color, and somewhat unusually hard and compact. 

 It shows no sign of oxidation by weathering, and in the actual specimens received 

 is packed with small stones which vary in size from about an inch and a half in 

 diameter downward. These lie in all positions, ami there is no apparent stratifi- 

 cation or lamination whatever, though here and there small parts of the whole 

 appear to be more arenaceous than the rest. None of the stones are perceptably 

 facetted, nor on these seen can any distinct striation be observed. They are either 

 subangular or fairly well-rounded in shape, and the surfaces of a few of them are 

 so smooth as to be described as polished. It is apparent, in fact, that they repre- 

 sent water-rounded material. 



The stones themselves consist almost exclusively of a hard, fine-grained, nearly 

 black material, which has not been microscopically examined in thin sections, but 

 appears to be undoubtedly a rather indurated argillite, resembling rocks seen by 

 the writer on several parts of the Alaskan coast, and which, merely from their 

 lithologic analogy with similar rocks on the better-known coast of British Colum- 

 bia, may represent what has been named the Vancouver Group, of Triassic Age. 



The material also contains rather numerous fragments of shells, but all so much 

 broken in the specimens actually received as to be impossible of exact determina- 

 tion. One small piece of a ribbed shell appears, however, to represent a small 

 specimen of Cardium blandum. Several fragments, when microscopically exam- 

 ined, were found to be slightly rounded on the broken edges, while others were 

 quite angular. The whole mass of the clay is more or less calcareous, effervescing 

 freely when an acid is applied. Though very hard when dry, fragments broken 

 from the inner surfaces of the specimens of bowlder-clay when placed in water 

 partially break up, and with the aid of agitation and occasional slight pressure 

 applied to the harder lumps the whole was easily and completely disintegrated. 



After removing the larger stones from about an ounce of the material, the residue 

 was subjected to a series of decantations at different intervals of time, by means of 

 which its constituents were separated in accordance with their size and specific 

 gravity, the modus operandi being the same as that employed in previous investi- 

 gations of bowlder-clays.* 



A microscopic examination of the various samples thus obtained, showed this 

 bowlder-clay to comprise a considerable proportion of very fine silty matter, of 

 which the particles are nearly equal in size ; also some formless argillaceous matter 

 and a larger proportion of sand. 



All grades of the sand proved to consist, to the amount of about one-third or one- 

 half, of partially or well rounded grains of the dark argillaceous rock above re- 

 ferred to, while the remainder was chiefly composed of quartz, generally glassy 

 and usually quite angular, though in part subangular or slightly rounded. 



Two samples of this sand, of medium grade, were kindly examined in detail by 

 Mr \V. F. Ferrier, who states that, in addition to the argillite grains, the con- 

 stituents of the coarser of these samples are as follows, in order of abundance : 



Medium coarse. — Quartz, feldspar (no striated grains were observed), magnetite, 

 a dark brown pyroxene (?), hornblende of various shades of green, brown mica, 

 (biotite ?) and a very few grains of titanite. 



Medium fine. — The same materials, but with mica and hornblende rather more 

 abundant than in the last. 



It may be added that the feldspar, pyroxene, hornblende, etc, are found in rather 



* Hull. Chicago Acad. Sci., vol. i, no < 



