This tweet by Daryl Blanks asks:

Day 1 VTMR trip @GeologyLeics -First stop Laxford bridge! gneiss with amphibolite and granitic pegmatite intrusions - can u spot all x-cutting relationships?!

What are cross-cutting relationships in this context, and how many are there?

enter image description here

  • $\begingroup$ @kwinkunks thanks for the edit. In some SE sites the term "bonus points" is understood to be a casual expression (thus the quotation marks) for an additional aspect of the question that's not required for an answer to be accepted. In this case the first answer seems to have addressed it, so your change to my question making it required is fine. $\endgroup$
    – uhoh
    Apr 14, 2018 at 23:01

1 Answer 1


Cross cutting relationships.

enter image description here

Here's a very rough sketch. You had the black stuff, which was then cross-cut by the red intrusion (grey in the original photo), and finally intruded by the blue intrusion (pink the in the original photo).

This is the law of superposition. For more fun follow #SuperpositionPuzzle on Twitter!

  • $\begingroup$ Thanks for your both colorful and informative answer! I'll enjoy the hashtag. Perhaps some day Stack Exchange will hots superpositionpuzzler, similar to codegolf ;-) $\endgroup$
    – uhoh
    Apr 14, 2018 at 11:21
  • 1
    $\begingroup$ @uhoh good idea actually - suggest it in meta $\endgroup$
    – Gimelist
    Apr 14, 2018 at 11:31
  • $\begingroup$ I don't have any standing in this field so I wouldn't be the right person to propose it myself, but I think the puzzler concept can certainly work well within the Stack Exchange ecosystem! I'd certainly love to see "science puzzlers" happen somehow! $\endgroup$
    – uhoh
    Apr 14, 2018 at 11:44

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