442 Transactions. — Geology. 



the sea, elevated sea-ledges and terraces, human records and 

 traditions. A subsidence of the land is more difficult to trace, 

 as each successive sea-margin is washed away or covered over 

 as the submergence continues. The existence of a submerged 

 forest, of fringing coral islands, or of fiords, may be regarded 

 as perfectly reliable evidence of subsidence. In studying the 

 oscillations of the earth it is necessary to guard against the 

 numerous causes of error that mav arise from the unceasing 

 struggle being waged between the land and sea. Neither 

 the encroachment of the sea on the shore-line, which may be 

 due to progressive erosion, nor the recession of the sea, which 

 may be due to local accumulations of alluvial detritus, are to 

 be accepted as evidence of subsidence without due considera- 

 tion. And, since secular elevation or depression of the land is 

 always taking place, it is obvious that an encroachment or 

 recession of the sea, due to denudation or reclamation, may 

 coincide with a geologic upheaval or depression. Therefore 

 in searching for proofs of such movements the student must 

 be on his guard against being deceived by any apparent 

 advance or recession of the sea. 



The great and varied assemblage of marine formations in 

 New Zealand, including representatives of nearly all ages, 

 affords ample proof that this country has been subject to 

 many alternating upheavals and subsidences in past geological 

 times. 



In the absence of human records it is impossible to 

 definitely or even approximately determine the direction of 

 the present secular movements on our shores. There is 

 abundant evidence that oscillations have taken place in com- 

 paratively recent times, but there are no data at our dis- 

 posal to enable us to ascertain whether the movements which 

 produced this evidence are still progressing in the same di- 

 rection. An upward motion may be succeeded by a period 

 of subsidence, and in the absence of a means of accurate 

 measurement it would not be safe to generalise on the evi- 

 dence of what has taken place in some past time, however 

 recent. 



The buried and submerged pine forests in the Thames 

 Valley and Bay of Plenty prove that the movement in those 

 regions has been downward up till a very recent date. The 

 extent of this area of subsidence cannot be defined, but the 

 geological evidence clearly indicates that it extended as far 

 west as the shores of Auckland Harbour. Whether this 

 secular subsidence of the Hauraki Gulf is still in progress 

 cannot be determined at present. 



A submerged forest on the sea-shore near Waitotara, with 

 the trunks of the trees still standing erect in the sea, points 

 to a very recent subsidence of the land in that region. The 



