462 Transactions. — Geology. 



looser material are washed down by the rain and spread out 

 in the form of fans along the beach. The harder portions 

 then tumble off and are rapidly' broken to pieces and carried 

 away by the action of tlie waves. The work of ei'osion here 

 must be rapid, for the prevailing westerly winds at times drive 

 in the waves with great fury. This strip of land, extending 

 from the Kaipara Heads to the Maunganui Bluff, and having a 

 width of about seven miles, appears to have its eastern limit 

 along the river. It is evidently the remains of a much larger 

 and higher area which at one time extended westward, and 

 has gradually been reduced to its present size under the 

 action of the weather and the sea. In none of the exposures 

 were any fossils to be seen, but the general appearance of the 

 rocks, their well-defined stratification, and the presence of a 

 band of compressed vegetation some 6 ft. or 8 ft. in thickness 

 outcropping at intervals for miles along the coast remove all 

 grounds for doubt as to their origin. The whole of this area 

 is an immense gumfield, and yet there are no kauri-trees to 

 be seen. The forests which must have covered it have long 

 since disappeared, and the land is now clothed with a stunted 

 growth consisting chiefly of fern, Lcptosi^ermum scopnrmm, 

 Lencojwgon fasciculaiuvi, L. fraseri, Pomaderris eliiptica, 

 P. filicifolia, and other plants usually found where these 

 comprise the prevailing vegetation. Tiie kauri seems to thrive 

 best on rugged, broken country where the elevation is con- 

 siderable. Any pronounced lowering of the general level 

 would bring about the destruction of the trees, and this is 

 apparently what has happened. As the land subsided the 

 forests died out, leaving behind these extensive deposits of 

 gum which of late years have become so valuable. These 

 beds of sandstone no doubt in formei' times had their eastern 

 extension along the flanks of the hills running north and 

 south on the left bank of the river, and overlay unconformably 

 portions of the older shales of which most of these hills con- 

 sist. The upper portion of this part of the series has now 

 been completely removed by the river, which in all probability 

 originally flowed along the junction of the older and younger 

 rocks, and hence carried away first those portions forming the 

 eastern extension of the beds. 



On the beach at the west coast is found an interesting 

 and valuable burrowing mollusc, Mesodesma ventricosa, known 

 locally as the " toheroa." In size it varies greatly, but 

 some of the larger forms measure as much as 6 m. by ^^m. 

 Its habitat occurs between high- and low-water mark — at 

 least, that is where it is found. When the tide is in it 

 comes to the surface of the sand, and, tiirusting out its 

 siphons, obtains the necessary nourishment from the sea- 

 water. As the waves retreat the siphons are withdrawn, and 



