Revieivs — W. S. W. Keiu — Tertiary Echinoids, Colorado. 281 



they are considered to be a product of the disintegration of the 

 Tertiary beds and the Chalk, and are assigned to the subaerial class. 

 Tlieir relation to the solid formation is discussed. 



The remaining superficial deposits — raised beach, gravels, and 

 brickearth — have apparently all been laid down in water. Two small 

 patches of raised beach aie mentioned, which rest a little below 

 100 feet O.D. Plateau gravels rest in patches on the Eocene beds at 

 altitudes between 30 and 315 feet; they are considered to be mainly 

 old river-deposits, and the various types are dealt with in detail. The 

 Valley Gravels are often chalky, when they are known as Combe 

 Hock ; they occur in all the principal valleys, and in this connexion 

 mention is made of the sheet of chalk and flint rubble which clothes 

 the southern slope of Portsdown. The brickearth is a brown loam 

 which thinly cloaks the edges of the Chalk and Eocene on the lower 

 steps of the coastal plain. 



In dealing with the Alluvium it is pointed out that by the close of 

 the Pleistocene period the larger rivers were running in valleys cut 

 down, through the gravel and brickearth-covered flats of the coastal 

 plain, to a depth of perhaps 20 or 30 feet below the ordinary high- 

 tide level of tlie present day, the coastline lying then farther to the 

 south. Subsidence has allowed the sea to advance once more north- 

 ward, drowning the lower reaches of the valleys, and filling them with 

 alluvial deposits. The mud and associated deposits are said to 

 attain a thickness of 35 feet at the Docks in Portsmouth Harbour 

 (south of the district). 



A chapter on economic aspects of the geology, including notes on 

 the water-supply, concludes the memoir. 



III. — Tertiaey Echinoids of the Caerizo Ceeek Eegion in the 

 CoLOEADO Deseet. By William S. W. Keav. University of 

 California Publications : Geology, Vol. VIII, No. 5, pp. 39-60, 

 pis. i-v. Berkeley, April 16, 1914. 

 rPHE Echinoid fauna of North America is known through a seriously 

 J. disjointed record. The marvellous profusion of Palaeozoic forms 

 cannot be matched in any other country, but Mesozoic types are 

 practically negligible. It is not until the later Tertiary stages are 

 reached that the history of Echinoid evolution is resumed, and tlien 

 in a few coastal regions only. Much of our knowledge of the fauna 

 of these relics of Tertiary subsidence is due to work carried out 

 under the auspices of the University of California. Bence it is that 

 the regions bordering on the GuH of California have given almost 

 the only evidence of American Cainozoic Echinoids. In view of the 

 extreme wealth of existing Echinoderm life in the shore waters of the 

 area, the study of the corresponding forms of a time not long past has 

 a peculiar interest. 



The age of the Carrizo formation, the horizon of the Echinoids 

 described in the paper under review, has not been precisely 

 determined. It has been correlated with the Etchegoin Series (of 

 Upper Miocene or Lower Pliocene age), but, as the writer indicates, 

 the Echinoid fauna is so nearly akin to the existing one of the 



