386 ON THE FAUNA AND BOTTOM-DEPOSITS NEAR THE 30-FM. LINE 



deposits around the Eddystone reef owe their coarse texture, in part at least, 

 to the intense wave action which prevents the accumuhition of the hner 

 particles, in part to the same intenser action which provides additional coarse 

 particles at the expense of the neighbouring submerged rock surfaces. 



"The finer deposits elsewhere are in more quiescent localities, with no 

 abrupt changes in the levels of the bottom to deflect the surface waves. 



" 105 and 106 (Ground XVII.) are subject to totally different geological 

 and other conditions, and more drcdgings from their locality would be 

 necessary to fully appreciate the circumstances affecting them. 



" It is to be noted that no rock fragments occur Avhich must have 

 necessarily, or have even probably, been drifted from the neighbouring shores, 

 guarding, however, the case of 105 and lOG, in which it is none the less quite 

 possible and even probable that the Archean schists underlie the gravels in 

 which they occur. 



" Three of the samples of silt have been approximately analysed, with the 



result set out in the following table. The results should be accurate to the 



nearest 0-25 per cent. 



Analysis of Silts. 



83 94 103 



Loss on Ignition. 



Bunsen . ll-50|oArn 12-00)oArA 12-50) „, ^.^ 



Blowpipe . Q.OOpO-^^ ■•■ 8.50}2^-"^<^ - S-bO^^-^^ 



SiOa . . 42-35 ... 35-42 ... 41-56 



AI2O3 . . 10-18 ... 9-64 ... 7-53 



FcgOg . . 9-29 ... 7-70 ... 8-00 



CaO' . . 13-67 ... 17-60 ... 12-69 



MgO . Heavy trace Heavy trace Heavy trace 



Undetermined 4-01 ... 9.14 ... 9-22 



" It is apparent that the CaO obtained in these analyses is more than can 



be accounted for by the organic CaCOg, the figures being : 



CaO in present analysis, CaO equivalent to organic 



per cent. CaC03, per cent. 



83 . . . 13-67 ... 9-24 



94 . . . 17-60 ... 10-45 



103 . . . 12-69 ... 11-85 



" On the other hand, the loss on ignition before blowpipe after previous 

 ignition over bunsen appears to roughly represent the COg in the organic 

 carbonate of lime. Thus : 



Additional loss on ignition over CO2 in CaCOj, per cent. 



blowpipe, per cent. 



83 . . . 9-00 ... 7-26 



94 . . . 8-50 ... • 8-21 



103 . . . 8-50 ... 9-31 



"The loss on ignition has accordingly been given in two figures, of which 

 the figure for loss over bunsen fairly represents the more volatile substances 

 and organic matter. 



