ABSTA'ACTS . 321 



While it is readily granted that such agents seem inadequate to 

 produce the effects observed, no others at all conriparable with them in 

 efficiency suggest themselves. And if the above conclusion is correct, 

 a solvent capable of removing a third of a quartz pebble an inch in 

 diameter, while still imbedded in its matrix, must be an extremely 

 important factor in gradation when acting under the much more fav- 

 orable conditions prevailing in the humus layer itself where the surface 

 exposed by the quartz grains is vastly greater in proportion to their 

 bulk and where the solvent action is not interrupted as it must be on 

 exposed rock surfaces. 



T/ie Crystalline and Mctamorphic Rocks of Northwcsf Georgia. By C. 

 WiLLARD Hayes and Alfred H. Brooks. 

 The region discussed in the paper extends southward loo miles 

 from the Tennessee line and westward twenty to eighty miles from the 

 Atlanta meridian. It embraces about 4000 square miles, forming a 

 belt to the east and south of the Georgia-Alabama Palaeozoic area. 

 The rocks of this region naturally fall into three groups : (i) the gran- 

 ites, gneisses and crystalline schists of the basal complex— probably 

 Archean; (2) the slates and conglomerates of the Ocoee series — prob- 

 ably Algonkian ; (3) intrusives in the other two series. 



The first group includes the Acworth gneiss, Austell granitoid 

 gneiss, Corbin granite and the Piedmont gneiss and crystalline schist. 

 In the second or clastic group only four members are distinguished 

 and formation names have not yet been assigned to them since this 

 classification is not regarded as final. These four members are {a) 

 basal conglomerate resting on the Corbin granite; {l>) black slate often 

 graphitic; {c) a series of interbedded slates and felspathic sandstones; 

 {d) garnetiferous slate probably an altered phase of {b) and (/). The 

 intrusives, which are found in association with members of both the 

 other groups, but most abundantly in a belt from ten to twenty miles 

 broad along their contact, named in the order of their intrusion, are 

 {a) amphibolite schists and diorite; (//) gabbro and basic greenstone 

 schist ; and (c) Villa Rica granite and associated coarse pegmatites. 



The above classification as well as the map accompanying the paper 

 is to be regarded as only preliminary since the necessary petrographic 

 study of the rocks has not yet been completed. The region discussed 

 is embraced within the limits of the Dalton, Cartersville, Marietta, 



