fine fraction may be partly carried out to sea and partly transported toward the head 

 of the bay by the bottom water to be deposited In the northern part of the bay and 

 on mud flats (Guilicher, 1958, p. 101; Johnson, 1925, p. 572). 



Oxidation of the agitated surface sediments may yield a lighter colored sedi- 

 ment, and the extraction of the fines leaves one that is coarser than the original . 

 The dark sediments in the northern sector probably indicate fine-grained sedimenta- 

 tion at present. Other explanations of the present sedimentary regime may be possible 

 however . 



At stations 29, 90, 128, 174, 178, and 189, masses and broken fragments of 

 hard silty cloy were found lying upon or partially mixed with the surface sediments. 

 (These fragments were removed from the samples in thp field.) The hard clay oc- 

 curred in curled and contorted plates, irregularly shqped masses, and angular 

 broken fragments. Some of the unfragmented samples are shown in Plate li . The 

 outer surfaces varied from hard, dark reddish -brown, to a soft, gray, sticky-clay 

 surface coating. The internal structure varied from banding parallel to the outer 

 surface, to massive and relatively structureless for the less hardened globs. The sam- 

 ples were generally riddled with holes, some apparently the result of solution or 

 erosion; however, most of the holes were formed prior to hardening and were caused 

 by burrowing organisms and by roots growing in the soft mud. Many of the holes 

 were encircled by bands of altered clay. 



The material was formed subaerially, probably on mud flats which supported 

 burrowing organisms and vegetation. The conditions leading to the development of 

 this material probably involved drying to form mud cracks and decaying of the vege- 

 tation originally growing in the mud. The decay of the plant roots caused oxidation 

 of the surrounding mud. The oxidation of the iron in the mud will account for the 

 color, banding, and hardness of the material (Rousseau, 1934). 



These deposits of hard clay may have arrived at their present position by flotation 

 on vegetation, ice-rafting, or rolling under certain conditions. Subsequent deposition 

 under water would result in fragmentation of most of the hardened masses due to differ- 

 ential expansion as the center of the mass became wet (Twenhofel, 1950, p .593) . 



In their present locations the hard-clay masses were found with crusts of bryo- 

 zoans and some attached brachiopods. Little, if any, sedimentation is presently 

 taking place at these locations. Zones and isolated occurrences of similar hard clay 

 were found in many of the cores. 



B. Sediment-Sonoprobe Correlation 



Direct correlation of vertical changes in sediment type and Sonoprobe sub- 

 bottom reflections was difficult in this area in spite of the numerous cores and grab 

 samples obtained. Fades changes, however, could be determined fairly accurate- 

 ly, and a determination of general sediment type, or lack of sediment, at a sampling 



35 



