OYSTEB BOTTOMS IN MATAGORDA RAY. 57 



41°. After March 1 the changes were more equable, a factor favor- 

 able to the young oyster fry, which appear to be peculiarly susceptible 

 to the influences of sudden transitions. There are no records avail- 

 able which show what the late spring and summer temperatures may 

 he, but it can be assumed that after the middle of April the tempera- 

 tures everywhere in the bay are above the minimum required for 

 spawning, and that there are few, if any, sudden changes such as kill 

 large numbers of the oyster fry and interfere with spawning on some 

 of the beds of the North Atlantic coast. 



DENSITIES OF WATER. 



By the density of the water is meant its specific gravity or the 

 weight of a given quantity, as compared with the weight of the same 

 quantity of pure fresh water. If the weight of the latter be con- 

 sidered as 1.000, that of salt water from the open sea will be about 

 1.02f>0, and the water on the oyster beds will be somewhere between 

 these two, as oysters live only in brackish waters and eventually die 

 if placed in water either too salt or too fresh. Aside from the ques- 

 tion of the very existence of the oyster the matter of density or salinity 

 influences the flavor, stock taken from the fresher waters being 

 insipid or even repugnant to many palates, while very salt water 

 produces a briny flavor equally objectionable. 



Two series of density observations were made during the survey, 

 one on the Fish Ha ivk in connection with the temperature observations 

 from January 1 to May 7, inclusive, and the other by the field party 

 as the work progressed from the head of the bay downward. The 

 latter, which, like the other series, have been corrected for tempera- 

 ture, are shown in red figures in their appropriate positions on the 

 chart, together with the date upon w r hich the observation was made. 

 As was to be expected, the water in the upper parts of the bay has a very 

 low density. The Colorado River, Caney Creek, and several smaller 

 streams flow into this part of the bay and at times discharge large 

 volumes of fresh water, and there is a considerable influx at all times. 

 This fresh water has no means of egress from the bay excepting at 

 Pass Cavallo, about 30 miles below Matagorda, and, moreover, its 

 escape is very materially retarded by Dog Island Reef, which with the 

 exception of several small channels forms a complete barrier across 

 the bay, with its crest awash at low water, just below T the mouth of 

 the Colorado. Formerly, as alread} T stated, a channel, Mitchells Cut, 

 afforded a connection of fluctuating breadth and depth between the 

 extreme upper part of the bay and the gulf, but in the summer of 

 1904, after man}' oscillations dating from the time of its formation 

 about 1875, this cut finally closed. It is apparent that during the 

 existence of the opening the density conditions in the upper bay must 

 have been quite different from those obtaining during the survey. It 



