Imagine the conversation that came before this response? Response: The summit has also been extensively worked.
Phone call:
 P1) What is the difference between the Birker Fell Formation and the Castle Crag?;
 P2) The Derwentwater fault runs along the valley of Broadslack Gill, the higher ground to the north west being mainly composed of the Birker Fell Formation.;
 P1) Are there any other interesting aspects about this article?;
 P2) These are plagioclase-phyric andesite lavas and subordinate sills.;
 P1) What are the differences between the two formations?;
 P2) By contrast Castle Crag shows outcropping of the Eagle Crag Member, a mixture of siltstone, sandstone, conglomerate and tuff with frequent andesite sills.;
 P1) Which is more dense?;
 P2) The slopes of Castle Crag are extensively quarried with pits and levels on the northern and south eastern flanks.;
 P1) Is there anything else that is notable about the two formations?;
 P2) 