kilohertz and 300 joules maximum power). The maximum depth below the 

 lake floor where reflections are recorded on the boomer system which has 

 the greater penetration potential, varies from to more than 37 meters 

 (120 feet). A "pinger" system achieved penetration of to 15 meters 

 (50 feet). 



In addition to seismic reflection profiles run during the geophysical 

 survey, a small pinger system (3.5 kilohertz; 25 joules) and side-scan 

 sonar were used during the coring phase of the operation to record condi- 

 tions in the immediate vicinity of each core site, and if time permitted, 

 to run a continuous line between adjacent core sites. These data proved 

 useful in assessing the bottom and very shallow subbottom conditions at 

 core sites. 



2. Core Boring . 



After preliminary inspection of seismic reflection profiles, 93 core 

 boring sites were selected. Cores at each of these sites were subse- 

 quently taken using a vibratory coring apparatus which obtains a nominal 

 8.9-centimeter-diameter (3.5 inches) core up to 6.1 meters (20 feet) in 

 length at full penetration. After visual inspection, representative 

 sediment samples were extracted from each core and grain-size distribu- 

 tions were measured by a rapid sediment analyzer (RSA) to determine the 

 hydraulic diameter of particles by measuring their fall velocity in water 

 (Schlee, 1966).^ Lithologic descriptions of samples and core logs were 

 also made by direct visual and microscopic examination of bulk properties 

 and constituent composition. 



3. Navigation Control . 



The position of the survey vessel and the coring platform was deter- 

 mined by a Mini Ranger III navigation system. This line-of-sight system 

 provides continuous location data from two shore stations to a master 

 station aboard the survey vessel. In general, fixes were recorded at 

 2-minute intervals throughout the seismic reflection survey. Because 

 of scale restrictions, only end fixes are shown on the survey coverage 

 charts in Figures 2 to 7. 



Because of the occasional loss of signal from the shore station to 

 the master station caused by the inability to maintain line-of-sight 

 between one of the shore stations and the survey vessel, the position 

 was sometimes best determined by dead-reckoning and range data from one 

 shore station. Also, since there was a lack of good horizontal survey 

 control in some areas along the shoreline, the shore stations were occu- 

 pied and the position plotted on a l:24,000-scale map sheet. The grid 

 values were then picked off the map sheet and used in the triangulation 

 calculations to determine the position of the survey vessel. The accu- 

 racy of the position fixes is estimated to be within ±30 meters (100 



^SCHLEE, J., "A Modified Woods Hole Rapid Sediment Analyzer," Journal 

 of Sedimentary Petrology, Vol. 36, No. 2, June 1966, pp. 403-413. 



15 



