Darwin and igneous rocks:
https://darwin-online.org.uk/content/frameset?pageseq=1&itemID=A860&viewtype=text&fbclid=IwY2xjawUV38JwZG9mBWV4dG4DYWVtAjEwAGJyaWQRMEFXR3g2T0RadERTU0xDZkVzcnRjBmFwcF9pZBAyMjIwMzkxNzg4MjAwODkyAAEeWCIXa1Wm1r5QqBV2qfAV2cW8LC02HK0sqsqwPrgbme_SSkfd6RgQfROBSL4_aem_ye3eSZCb25_bXM9iFAZ7Jw