Pirsson and Washington — Geology of New Hampshire. 349 



and absorption of the country rock with which the mass of 

 syenite magma came in contact for two sufficient and convinc- 

 ing reasons. First, because as already shown, the surrounding 

 rocks differ widely in character and in chemical composition in 

 different places, while the granite border maintains everywhere 

 essentially the same characters, and second, because in many 

 places inclusions of the country rock are to be seen in it which, 

 without regard to size, preserve all the sharpness and angularity 

 of their original fragmentary form, thus showing that, although 

 they have been much metamorphosed, melting of them did 

 not occur. On the highest peaks and ridges and in the deepest 

 erosive cuts into the mass it has been worn away and the main 

 type of syenite appears. Its thickness was quite variable, and 

 in a few places it did not appear at all. The line between the 

 syenite and granite as shown on the geological map is therefore 

 to_be taken as a generalized expression of the existence of the 

 two types and not as a definite geological boundary line, since 

 for reasons just given this could not be definitely determined. 



Gilford diorite area. — On our first visit to the region we 

 found quite abundantly distributed in the form of bowlders 

 in the fields and stone walls of the fences along the higher part 

 of the land from Gilford over to West Alton, a most peculiar 

 dark rock composed of large dark-brown hornblendes poikiliti- 

 cally enclosing ophitic feldspars. In field usage it is here 

 called a diorite for purposes of geologic description ; petro- 

 graphically it is, as will be shown later, a grano-hornblende- 

 camptonose, or in the older systems an essexite. On our 

 second visit an especial search was made to locate if possible 

 the occurrence of this type, and it was found to constitute a 

 considerable mass on the lower west slope of Locke's Hill and 

 not far from the Gilford station on the railway. Its area is 

 small, probably not over half a mile in length north and south 

 along the slope and less than that in breadth. On the north it 

 rises in heavy ledges above a little spring drainage and on the 

 west its lower slopes are covered with soil and debris, but 

 above this it forms a rather well-defined bench on the lower 

 mountain side and in rather prominent outcrops it is seen 

 everywhere over the pasture fields which lie upon it. On the 

 south it descends into a little ravine, a locality mentioned 

 above in connection with the syenite, and is here in contact 

 with the mica schists and gneisses. Its upper edge is in con- 

 tact with the syenite, but the actual contact was everywhere 

 covered so far as we could discover. We have traced it, how- 

 ever, to within a few yards distance, and it is then observed 

 that the rock diminishes very strikingly in the size of its grain, 

 especially so with regard to the large poikilitic hornblendes, 

 and for this reason and others to be mentioned later we believe 



