BRITISH COLUMBIA COXCKETIOXS " 619 



The laminated, very fine-textured sediments in which these concre- 

 tions have developed afford in texture a close approach to this ideal 

 homogeneous medium for symmetrical concretionary' growth within the 

 limits of the individual strata. The planes separating these layers mark 

 the vertical limits of the complete homogeneity which characterizes each 

 stratum and produce discoid forms instead of the spheres which a cla}' 

 homogeneous both vertically and horizontally would produce. The fine 

 lamination of the clay interrupts in a degree its homogeneity. This in- 

 terruption coincides with a series of horizontal planes corresponding to 

 the boundaries between the laminae. Between the limits of any two of 

 these planes the homogeneity is perfect or nearly so and results in the 

 discoid or subdiscoid symmetry of the several units in the forms repre- 

 sented by figures 3 to 6, plate 7. Slight differences in the composition 

 of the different laminse which supplied the material for the several disks 

 of a concretion, contrasts in the degree of water saturation of the several 

 laminae concerned in the growth of a given concretion, and variations in 

 the gTound water level were probably all factors in the development of 

 the compound discoid forms, which are composed of a series of disks 

 varying greatly in size. 



Dr. George Hanson has furnished, at the writer's suggestion, the fol- 

 lowing notes on the field relations of the Endako concretions : 



•'The concretions are found on the banks of a small creek about 1 mile west 

 of Endako, British Columbia. Clay banks containing concretions are known 

 to extend for about one-half mile along the creek. Small landslides have ex- 

 posed the clay in several places. The banks are nowhere more than 50 feet 

 above the bed of the creek and the surrounding country is flat or rolling. 

 Going north from the railway along the creek, the first slide reached exposes 

 stratified clays and sandy clays. The second, third, and fourth slides are 

 reached at intervals of 200, 300, and 500 yards and all consist of similar 

 material. 



"As seen from the railway, the country appears to be of very low relief for 

 75 miles west and for 100 miles east of Endako. The rocks seen are chiefly 

 l)oulder clay and other morainal material. Stratified clays are occasionally 

 seen. The clays at Endako are horizontal and are very well stratified. They 

 are not overlain by any glacial material. The base is unexposed, but glacial 

 deposits are inferred from the abmidance of boulder clay in the vicinity. The 

 clays are probably of late Pleistocene or early Recent age. 



"The strata in the Endako clays ^ary from paper-thin lamin;e to 8-inch 

 beds. The sandy clays and sands are commonly in 1 to 4 inch bands. 



•'There is a marked gradation in the shape of the concretions in a north- 

 south line. The most southerly slide contains flat disks, flat ovals, and numer- 

 ous irregular branching flat concretions. In the second slide the concretions 

 are more regular. Tlie fourth slide contains a few irregular concretions and 

 all the good chessman type of concretions. None of the perfect ones were 



